description: This is the easy version of the problem. The only difference between the two versions is the constraint on n. You can make hacks only if all versions of the problem are solved.
  
  A forest is an undirected graph without cycles (not necessarily connected).
  
  Mocha and Diana are friends in Zhijiang, both of them have a forest with nodes numbered from 1 to n, and they would like to add edges to their forests such that: 
  
    * After adding edges, both of their graphs are still forests. 
    * They add the same edges. That is, if an edge (u, v) is added to Mocha's forest, then an edge (u, v) is added to Diana's forest, and vice versa. 
  
  
  
  Mocha and Diana want to know the maximum number of edges they can add, and which edges to add.
  
  Input
  
  The first line contains three integers n, m_1 and m_2 (1 ≤ n ≤ 1000, 0 ≤ m_1, m_2 < n) — the number of nodes and the number of initial edges in Mocha's forest and Diana's forest.
  
  Each of the next m_1 lines contains two integers u and v (1 ≤ u, v ≤ n, u ≠ v) — the edges in Mocha's forest.
  
  Each of the next m_2 lines contains two integers u and v (1 ≤ u, v ≤ n, u ≠ v) — the edges in Diana's forest.
  
  Output
  
  The first line contains only one integer h, the maximum number of edges Mocha and Diana can add (in each forest).
  
  Each of the next h lines contains two integers u and v (1 ≤ u, v ≤ n, u ≠ v) — the edge you add each time.
  
  If there are multiple correct answers, you can print any one of them.
  
  Examples
  
  Input
  
  
  3 2 2
  1 2
  2 3
  1 2
  1 3
  
  
  Output
  
  
  0
  
  
  Input
  
  
  5 3 2
  5 4
  2 1
  4 3
  4 3
  1 4
  
  
  Output
  
  
  1
  2 4
  
  
  Input
  
  
  8 1 2
  1 7
  2 6
  1 5
  
  
  Output
  
  
  5
  5 2
  2 3
  3 4
  4 7
  6 8
  
  Note
  
  In the first example, we cannot add any edge.
  
  In the second example, the initial forests are as follows.
  
  <image>
  
  We can add an edge (2, 4).
  
  <image>
solution: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.util.*;
  import java.util.stream.IntStream;
  
  
  public class Main implements Runnable {
      int n, m, k;
      static boolean use_n_tests = false;
      long mod = 1_000_000_007;
      long mod1 = 998244353L;
  
      void solve(FastScanner in, PrintWriter out, int testNumber) {
          n = in.nextInt();
          int m1 = in.nextInt();
          int m2 = in.nextInt();
          DisjointSets d1 = new DisjointSets(n);
          int k = n - 1 - Math.max(m1, m2);
          out.println(k);
          for (int i = 0; i < m1; i++) {
              int v = in.nextInt() - 1;
              int u = in.nextInt() - 1;
              d1.unite(v, u);
          }
  
          DisjointSets d2 = new DisjointSets(n);
          for (int i = 0; i < m2; i++) {
              int v = in.nextInt() - 1;
              int u = in.nextInt() - 1;
              d2.unite(v, u);
          }
  
          for (int j = 1; j < n && k > 0; j++) {
              int v = 0;
              int u = j;
              if (d1.root(v) != d1.root(u) && d2.root(v) != d2.root(u)) {
                  d1.unite(v, u);
                  d2.unite(v, u);
                  out.printf("%d %d\n", v + 1, u + 1);
                  k--;
              }
          }
  
          List<Integer> left = new ArrayList<>(), right = new ArrayList<>();
          int it = 0, it1 = 0;
          for (int i = 1; i < n && k > 0; i++) {
              if (d1.root(0) != d1.root(i)) {
                  d1.unite(0, i);
                  left.add(i);
              }
              if (d2.root(0) != d2.root(i)) {
                  d2.unite(0, i);
                  right.add(i);
              }
              if (it < left.size() && it1 < right.size()) {
                  out.printf("%d %d\n", left.get(it++) + 1, right.get(it1++) + 1);
                  k--;
              }
          }
      }
  
      public class DisjointSets {
          int[] p;
  
          DisjointSets(int size) {
              p = new int[size];
              for (int i = 0; i < size; i++)
                  p[i] = i;
          }
  
          public int root(int x) {
              return x == p[x] ? x : (p[x] = root(p[x]));
          }
  
          public void unite(int a, int b) {
              a = root(a);
              b = root(b);
              if (a != b)
                  p[a] = b;
          }
      }
  
      char rev(char c) {
          if (c == 'R') {
              return 'B';
          }
          return 'R';
      }
  
      // ****************************** template code ***********
  
      boolean triangleCheck(int a, int b, int c) {
          return a + b > c && a + c > b && b + c > a;
      }
  
      Map<Integer, Integer> numberCompression(List<Integer> ls) {
          Collections.sort(ls);
          int id = 1;
          Map<Integer, Integer> comp = new HashMap<>();
          for (int num : ls) {
              if (!comp.containsKey(num)) {
                  comp.put(num, id++);
              }
          }
          return comp;
      }
  
      long lcm(long a, long b) {
          return (a / gcd(a, b)) * b;
      }
  
      long gcd(long a, long b) {
          return b == 0 ? a : gcd(b, a % b);
      }
  
      class Pt {
          int x, y;
  
          boolean sameAxis(Pt b) {
              return b.x == x || b.y == y;
          }
  
          int manxDist(Pt b) {
              return Math.abs(x - b.x) + Math.abs(y - b.y);
          }
  
          void read() {
              x = in.nextInt();
              y = in.nextInt();
          }
      }
  
      void swap(Integer[] a, int i, int j) {
          Integer tmp = a[i];
          a[i] = a[j];
          a[j] = tmp;
      }
  
      void swap(List<Integer> a, int i, int j) {
          Integer tmp = a.get(i);
          a.set(i, a.get(j));
          a.set(j, tmp);
      }
  
      long manhDist(long x, long y, long x1, long y1) {
          return Math.abs(x - x1) + Math.abs(y - y1);
      }
  
      double dist(double x, double y, double x1, double y1) {
          return Math.sqrt(Math.pow(x - x1, 2.0) + Math.pow(y - y1, 2.0));
      }
  
      public static class FW {
          public static void add(long[] t, int i, long value) {
              for (; i < t.length; i |= i + 1)
                  t[i] += value;
          }
  
          public static long sum(long[] t, int i) {
              long res = 0;
              for (; i >= 0; i = (i & (i + 1)) - 1)
                  res += t[i];
              return res;
          }
  
          public static void add(long[] t, int a, int b, long value) {
              add(t, a, value);
              add(t, b + 1, -value);
          }
      }
  
      int sign(int a) {
          if (a < 0) {
              return -1;
          }
          return 1;
      }
  
      long binpow(long a, int b) {
          long res = 1;
          while (b != 0) {
              if (b % 2 == 0) {
                  b /= 2;
                  a *= a;
                  a %= mod;
              }
  
              b--;
              res *= a;
              res %= mod;
          }
          return res;
      }
  
      List<Integer> getDigits(long n) {
          List<Integer> res = new ArrayList<>();
          while (n != 0) {
              res.add((int) (n % 10L));
              n /= 10;
          }
          return res;
      }
  
      List<Integer> generatePrimes(int n) {
          List<Integer> res = new ArrayList<>();
          boolean[] sieve = new boolean[n + 1];
          for (int i = 2; i <= n; i++) {
              if (!sieve[i]) {
                  res.add(i);
              }
              if ((long) i * i <= n) {
                  for (int j = i * i; j <= n; j += i) {
                      sieve[j] = true;
                  }
              }
          }
          return res;
      }
  
      int[] ask(int l) {
          System.out.printf("? %d\n", l);
          System.out.flush();
          return in.nextArray(n);
      }
  
      static int stack_size = 1 << 29;
  
      static class Coeff {
          long mod;
          long[][] C;
          long[] fact;
          boolean cycleWay = false;
  
          Coeff(int n, long mod) {
              this.mod = mod;
              fact = new long[n + 1];
              fact[0] = 1;
              for (int i = 1; i <= n; i++) {
                  fact[i] = i;
                  fact[i] %= mod;
                  fact[i] *= fact[i - 1];
                  fact[i] %= mod;
              }
          }
  
          Coeff(int n, int m, long mod) {
              // n > m
              cycleWay = true;
              this.mod = mod;
              C = new long[n + 1][m + 1];
              for (int i = 0; i <= n; i++) {
                  for (int j = 0; j <= Math.min(i, m); j++) {
                      if (j == 0 || j == i) {
                          C[i][j] = 1;
                      } else {
                          C[i][j] = C[i - 1][j - 1] + C[i - 1][j];
                          C[i][j] %= mod;
                      }
                  }
              }
          }
  
          public long C(int n, int m) {
              if (cycleWay) {
                  return C[n][m];
              }
              return fC(n, m);
          }
  
          private long fC(int n, int m) {
              return (fact[n] * inv(fact[n - m] * fact[m] % mod)) % mod;
          }
  
          private long inv(long r) {
              if (r == 1)
                  return 1;
              return ((mod - mod / r) * inv(mod % r)) % mod;
          }
      }
  
      class Pair {
          int first;
          long second;
  
          Pair(int f, long s) {
              first = f;
              second = s;
          }
  
          public int getFirst() {
              return first;
          }
  
          public long getSecond() {
              return second;
          }
      }
  
      class MultisetTree<T> {
          int size = 0;
  
          TreeMap<T, Integer> mp = new TreeMap<>();
  
          void add(T x) {
              mp.merge(x, 1, Integer::sum);
              size++;
          }
  
          void remove(T x) {
              if (mp.containsKey(x)) {
                  mp.merge(x, -1, Integer::sum);
                  if (mp.get(x) == 0) {
                      mp.remove(x);
                  }
                  size--;
              }
          }
  
          boolean contains(T x) {
              return mp.containsKey(x);
          }
  
          T greatest() {
              return mp.lastKey();
          }
  
          T higher(T x) {
              return mp.higherKey(x);
          }
  
          T smallest() {
              return mp.firstKey();
          }
  
          int size() {
              return size;
          }
  
          int diffSize() {
              return mp.size();
          }
      }
  
      class Multiset<T> {
          int size = 0;
  
          Map<T, Integer> mp = new HashMap<>();
  
          void add(T x) {
              mp.merge(x, 1, Integer::sum);
              size++;
          }
  
          boolean contains(T x) {
              return mp.containsKey(x);
          }
  
          void remove(T x) {
              if (mp.containsKey(x)) {
                  mp.merge(x, -1, Integer::sum);
                  if (mp.get(x) == 0) {
                      mp.remove(x);
                  }
                  size--;
              }
          }
  
          int size() {
              return size;
          }
  
          int diffSize() {
              return mp.size();
          }
      }
  
      static class Range {
          int l, r;
          int id;
  
          public int getL() {
              return l;
          }
  
          public int getR() {
              return r;
          }
  
          public Range(int l, int r, int id) {
              this.l = l;
              this.r = r;
              this.id = id;
          }
      }
  
      static class Array {
          static Range[] readRanges(int n, FastScanner in) {
              Range[] result = new Range[n];
              for (int i = 0; i < n; i++) {
                  result[i] = new Range(in.nextInt(), in.nextInt(), i);
              }
              return result;
          }
  
          static List<List<Integer>> intInit2D(int n) {
              List<List<Integer>> res = new ArrayList<>();
              for (int i = 0; i < n; i++) {
                  res.add(new ArrayList<>());
              }
              return res;
          }
  
          static boolean isSorted(Integer[] a) {
              for (int i = 0; i < a.length - 1; i++) {
                  if (a[i] > a[i + 1]) {
                      return false;
                  }
              }
              return true;
          }
  
          static public long sum(int[] a) {
              long sum = 0;
              for (int x : a) {
                  sum += x;
              }
              return sum;
          }
  
          static public long sum(long[] a) {
              long sum = 0;
              for (long x : a) {
                  sum += x;
              }
              return sum;
          }
  
          static public long sum(Integer[] a) {
              long sum = 0;
              for (int x : a) {
                  sum += x;
              }
              return sum;
          }
  
          static public int min(Integer[] a) {
              int mn = Integer.MAX_VALUE;
              for (int x : a) {
                  mn = Math.min(mn, x);
              }
              return mn;
          }
  
          static public int min(int[] a) {
              int mn = Integer.MAX_VALUE;
              for (int x : a) {
                  mn = Math.min(mn, x);
              }
              return mn;
          }
  
          static public int max(Integer[] a) {
              int mx = Integer.MIN_VALUE;
              for (int x : a) {
                  mx = Math.max(mx, x);
              }
              return mx;
          }
  
          static public int max(int[] a) {
              int mx = Integer.MIN_VALUE;
              for (int x : a) {
                  mx = Math.max(mx, x);
              }
              return mx;
          }
  
          static public int[] readint(int n, FastScanner in) {
              int[] out = new int[n];
              for (int i = 0; i < out.length; i++) {
                  out[i] = in.nextInt();
              }
              return out;
          }
      }
  
      class Graph {
          List<List<Integer>> graph;
  
          Graph(int n) {
              create(n);
          }
  
          private void create(int n) {
              List<List<Integer>> graph = new ArrayList<>();
              for (int i = 0; i < n; i++) {
                  graph.add(new ArrayList<>());
              }
              this.graph = graph;
          }
  
          int size() {
              return graph.size();
          }
  
          List<Integer> abj(int v) {
              return graph.get(v);
          }
  
          void read(int m, FastScanner in) {
              for (int i = 0; i < m; i++) {
                  int v = in.nextInt() - 1;
                  int u = in.nextInt() - 1;
                  graph.get(v).add(u);
              }
          }
  
          void readBi(int m, FastScanner in) {
              for (int i = 0; i < m; i++) {
                  int v = in.nextInt() - 1;
                  int u = in.nextInt() - 1;
                  graph.get(v).add(u);
                  graph.get(u).add(v);
              }
          }
      }
  
      class FastScanner {
          BufferedReader br;
          StringTokenizer st;
  
          public FastScanner(InputStream io) {
              br = new BufferedReader(new InputStreamReader(io));
          }
  
          public String line() {
              String result = "";
              try {
                  result = br.readLine();
              } catch (IOException e) {
                  e.printStackTrace();
              }
              return result;
          }
  
          public String next() {
              while (st == null || !st.hasMoreElements()) {
                  try {
                      st = new StringTokenizer(br.readLine());
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
  
          public char[] nextc() {
              return next().toCharArray();
          }
  
          public int nextInt() {
              return Integer.parseInt(next());
          }
  
          public int[] nextArray(int n) {
              int[] res = new int[n];
              for (int i = 0; i < n; i++) {
                  res[i] = in.nextInt();
              }
              return res;
          }
  
          public long[] nextArrayL(int n) {
              long[] res = new long[n];
              for (int i = 0; i < n; i++) {
                  res[i] = in.nextLong();
              }
              return res;
          }
  
          public Long[] nextArrayL2(int n) {
              Long[] res = new Long[n];
              for (int i = 0; i < n; i++) {
                  res[i] = in.nextLong();
              }
              return res;
          }
  
  
          public Integer[] nextArray2(int n) {
              Integer[] res = new Integer[n];
              for (int i = 0; i < n; i++) {
                  res[i] = in.nextInt();
              }
              return res;
          }
  
          public long nextLong() {
              return Long.parseLong(next());
          }
  
      }
  
      void run_t_tests() {
          int t = in.nextInt();
          int i = 0;
          while (t-- > 0) {
              solve(in, out, i++);
          }
      }
  
      void run_one() {
          solve(in, out, -1);
      }
  
      @Override
      public void run() {
          in = new FastScanner(System.in);
          out = new PrintWriter(System.out);
          if (use_n_tests) {
              run_t_tests();
          } else {
              run_one();
          }
          out.close();
      }
  
      static FastScanner in;
      static PrintWriter out;
  
      public static void main(String[] args) throws InterruptedException {
          Thread thread = new Thread(null, new Main(), "", stack_size);
          thread.start();
          thread.join();
      }
  }