description: The numbers 1,   2,   ...,   n ⋅ k are colored with n colors. These colors are indexed by 1,   2,   ...,   n. For each 1 ≤ i ≤ n, there are exactly k numbers colored with color i.
  
  Let [a,   b] denote the interval of integers between a and b inclusive, that is, the set \\{a,   a + 1,   ...,   b\}. You must choose n intervals [a_1,   b_1],   [a_2,   b_2],   ..., [a_n,   b_n] such that: 
  
    * for each 1 ≤ i ≤ n, it holds 1 ≤ a_i < b_i ≤ n ⋅ k; 
    * for each 1 ≤ i ≤ n, the numbers a_i and b_i are colored with color i; 
    * each number 1 ≤ x ≤ n ⋅ k belongs to at most \left⌈ (n)/(k - 1) \right⌉ intervals. 
  
  
  
  One can show that such a family of intervals always exists under the given constraints.
  
  Input
  
  The first line contains two integers n and k (1 ≤ n ≤ 100, 2 ≤ k ≤ 100) — the number of colors and the number of occurrences of each color.
  
  The second line contains n ⋅ k integers c_1,   c_2,   ...,   c_{nk} (1 ≤ c_j ≤ n), where c_j is the color of number j. It is guaranteed that, for each 1 ≤ i ≤ n, it holds c_j = i for exactly k distinct indices j.
  
  Output
  
  Output n lines. The i-th line should contain the two integers a_i and b_i.
  
  If there are multiple valid choices of the intervals, output any.
  
  Examples
  
  Input
  
  
  4 3
  2 4 3 1 1 4 2 3 2 1 3 4
  
  
  Output
  
  
  4 5
  1 7
  8 11
  6 12
  
  Input
  
  
  1 2
  1 1
  
  
  Output
  
  
  1 2
  
  
  Input
  
  
  3 3
  3 1 2 3 2 1 2 1 3
  
  
  Output
  
  
  6 8
  3 7
  1 4
  
  Input
  
  
  2 3
  2 1 1 1 2 2
  
  
  Output
  
  
  2 3
  5 6
  
  Note
  
  In the first sample, each number can be contained in at most \left⌈ (4)/(3 - 1) \right⌉ = 2 intervals. The output is described by the following picture:
  
  <image>
  
  In the second sample, the only interval to be chosen is forced to be [1,   2], and each number is indeed contained in at most \left⌈ (1)/(2 - 1) \right⌉ = 1 interval.
  
  In the third sample, each number can be contained in at most \left⌈ (3)/(3 - 1) \right⌉ = 2 intervals. The output is described by the following picture:
  
  <image>
solution: import java.io.OutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintWriter;
  import java.util.Objects;
  import java.util.Arrays;
  import java.util.Map;
  import java.util.HashMap;
  import java.util.InputMismatchException;
  import java.io.IOException;
  import java.io.InputStream;
  
  /**
   * Built using CHelper plug-in
   * Actual solution is at the top
   */
  public class Main {
      public static void main(String[] args) {
          InputStream inputStream = System.in;
          OutputStream outputStream = System.out;
          InputReader in = new InputReader(inputStream);
          PrintWriter out = new PrintWriter(outputStream);
          ETsvetaIOtrezki solver = new ETsvetaIOtrezki();
          solver.solve(1, in, out);
          out.close();
      }
  
      static class ETsvetaIOtrezki {
          public void solve(int testNumber, InputReader in, PrintWriter out) {
              int n = in.nextInt();
              int k = in.nextInt();
              int[] a = new int[n * k];
  
              int m = (n + k - 2) / (k - 1);
  
              int[] prev = new int[n];
              int[] ct = new int[n * k];
  
              Arrays.fill(prev, -1);
              Map<Integer, Pair<Integer, Integer>> ans = new HashMap<>();
  
  
              for (int i = 0; i < n * k; i++) {
                  int val = in.nextInt() - 1;
                  if (prev[val] != -1 && !ans.containsKey(val)) {
                      int max = Integer.MIN_VALUE;
  
                      for (int h = prev[val]; h <= i; h++) {
                          ct[h]++;
                          max = Math.max(max, ct[h]);
                      }
                      if (max <= m) {
                          ans.put(val, Pair.of(prev[val], i));
                      } else {
                          for (int h = prev[val]; h <= i; h++) {
                              ct[h]--;
                          }
                      }
                  }
                  prev[val] = i;
              }
              for (int i = 0; i < n; i++) {
                  Pair<Integer, Integer> p = ans.get(i);
                  out.println((p.fs + 1) + " " + (p.sc + 1));
              }
          }
  
      }
  
      static class InputReader {
          private static final int BUFFER_LENGTH = 1 << 10;
          private InputStream stream;
          private byte[] buf = new byte[BUFFER_LENGTH];
          private int curChar;
          private int numChars;
  
          public InputReader(InputStream stream) {
              this.stream = stream;
          }
  
          private int nextC() {
              if (numChars == -1) {
                  throw new InputMismatchException();
              }
              if (curChar >= numChars) {
                  curChar = 0;
                  try {
                      numChars = stream.read(buf);
                  } catch (IOException e) {
                      throw new InputMismatchException();
                  }
                  if (numChars <= 0)
                      return -1;
              }
              return buf[curChar++];
          }
  
          public int nextInt() {
              int c = skipWhileSpace();
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = nextC();
              }
              int res = 0;
              do {
                  if (c < '0' || c > '9') {
                      throw new InputMismatchException();
                  }
                  res *= 10;
                  res += c - '0';
                  c = nextC();
              } while (!isSpaceChar(c));
              return res * sgn;
          }
  
          public int skipWhileSpace() {
              int c = nextC();
              while (isSpaceChar(c)) {
                  c = nextC();
              }
              return c;
          }
  
          public boolean isSpaceChar(int c) {
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
  
      }
  
      static class Pair<T, K> {
          T fs;
          K sc;
  
          public Pair(T fs, K sc) {
              this.fs = fs;
              this.sc = sc;
          }
  
          public static <T, K> Pair<T, K> of(T fs, K sc) {
              return new Pair<>(fs, sc);
          }
  
          public boolean equals(Object o) {
              if (this == o) {
                  return true;
              }
              if (o == null || getClass() != o.getClass()) {
                  return false;
              }
              Pair<?, ?> pair = (Pair<?, ?>) o;
              return Objects.equals(fs, pair.fs) && Objects.equals(sc, pair.sc);
          }
  
          public int hashCode() {
              return Objects.hash(fs, sc);
          }
  
      }
  }
  
  