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.util.*;
  import java.io.*;
  import static java.lang.Math.min;
  import static java.lang.Math.abs;
  import static java.lang.Math.max;
  public class EdE {
  	static long[] mods = {1000000007, 998244353, 1000000009};
  	static long mod = mods[0];
  	public static MyScanner sc;
      public static PrintWriter out;
  	public static void main(String[] largewang) throws Exception{
  		// TODO Auto-generated method stub
   		sc = new MyScanner();
   		out = new PrintWriter(System.out);
   	
   			int n = sc.nextInt();
   			int k = sc.nextInt();
   			int[] arr = readArrayInt(n*k);
   			int[] next = new int[n*k];
   			int[] lastSeen = new int[n+1];
   			Arrays.fill(lastSeen, -1);
   			for(int j = n*k-1;j>=0;j--){
  				next[j] = lastSeen[arr[j]];
  				lastSeen[arr[j]] = j;
   			}
   			Map<Integer, Integer> l = new HashMap<>();
   			Map<Integer, Integer> r = new HashMap<>();
   			for(int start = 1;start <= n;start+=(k-1)){// start to start+k-2
   				ArrayList<Pair> temp = new ArrayList<>();
   				for(int j = 0;j<n*k;j++){
   					
   					if (arr[j] >= start && arr[j] <= start+k-2){
   						temp.add(new Pair(j, arr[j]));
   					}
   				}
  				HashSet<Integer> left = new HashSet<>();
  				for(int j = start;j<=start+k-2;j++){
  					left.add(j);
  				}
  				HashMap<Integer, Integer> currRun = new HashMap<>();
  				for(int j = 0;j<temp.size();j++){
  					if (!left.contains(temp.get(j).val))
  						continue;
  					if (!currRun.containsKey(temp.get(j).val)) {
  						currRun.put(temp.get(j).val, temp.get(j).index);
  					} else {
  						l.put(temp.get(j).val, currRun.get(temp.get(j).val));
  						r.put(temp.get(j).val, temp.get(j).index);
  						left.remove(temp.get(j).val);
  						currRun.clear();
  					}
  				}
   			}
   			for(int j = 1;j<=n;j++){
   				out.println((l.get(j)+1) + " " + (r.get(j)+1));
   			}
   			out.println();
   		
   		out.close();
   		
   	}
  	static class Pair{
  		private int index;
  		private int val;
  		public Pair(int index, int val) {
  			this.index = index;
  			this.val = val;
  			
  		}
  	}
  	public static void sort(int[] array){
  		ArrayList<Integer> copy = new ArrayList<>();
  		for (int i : array)
  			copy.add(i);
  		Collections.sort(copy);
  		for(int i = 0;i<array.length;i++)
  			array[i] = copy.get(i);
  	}
  	static String[] readArrayString(int n){
  		String[] array = new String[n];
  		for(int j =0 ;j<n;j++)
  			array[j] = sc.next();
  		return array;
  	}
  	static int[] readArrayInt(int n){
      	int[] array = new int[n];
      	for(int j = 0;j<n;j++)
      		array[j] = sc.nextInt();
      	return array;
      }
  	static int[] readArrayInt1(int n){
  		int[] array = new int[n+1];
  		for(int j = 1;j<=n;j++){
  			array[j] = sc.nextInt();
  		}
  		return array;
  	}
  	static long[] readArrayLong(int n){
  		long[] array = new long[n];
  		for(int j =0 ;j<n;j++)
  			array[j] = sc.nextLong();
  		return array;
  	}
  	static double[] readArrayDouble(int n){
  		double[] array = new double[n];
  		for(int j =0 ;j<n;j++)
  			array[j] = sc.nextDouble();
  		return array;
  	}
  	static int minIndex(int[] array){
  		int minValue = Integer.MAX_VALUE;
  		int minIndex = -1;
  		for(int j = 0;j<array.length;j++){
  			if (array[j] < minValue){
  				minValue = array[j];
  				minIndex = j;
  			}
  		}
  		return minIndex;
  	}
  	static int minIndex(long[] array){
  		long minValue = Long.MAX_VALUE;
  		int minIndex = -1;
  		for(int j = 0;j<array.length;j++){
  			if (array[j] < minValue){
  				minValue = array[j];
  				minIndex = j;
  			}
  		}
  		return minIndex;
  	}
  	static int minIndex(double[] array){
  		double minValue = Double.MAX_VALUE;
  		int minIndex = -1;
  		for(int j = 0;j<array.length;j++){
  			if (array[j] < minValue){
  				minValue = array[j];
  				minIndex = j;
  			}
  		}
  		return minIndex;
  	}
  	static long power(long x, long y){
  		if (y == 0)
  			return 1;
  		if (y%2 == 1)
  			return (x*power(x, y-1))%mod;
  		return power((x*x)%mod, y/2)%mod;
  	}
  	static void verdict(boolean a){
          out.println(a ? "YES" : "NO");
      }
      public static class MyScanner {
          BufferedReader br;
          StringTokenizer st;
          public MyScanner() {
              br = new BufferedReader(new InputStreamReader(System.in));
          }
          String next() {
              while (st == null || !st.hasMoreElements()) {
                  try {
                      st = new StringTokenizer(br.readLine());
                  } 
                  catch (IOException e) {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
          int nextInt() {
              return Integer.parseInt(next());
          }
          long nextLong() {
              return Long.parseLong(next());
          }
          double nextDouble() {
              return Double.parseDouble(next());
          }
          String nextLine() {
              String str = "";
              try{
                  str = br.readLine();
              } 
              catch (IOException e) {
                  e.printStackTrace();
              }
              return str;
          }
          
      }	
  }
  
  //StringJoiner sj = new StringJoiner(" "); 
  //sj.add(strings)
  //sj.toString() gives string of those stuff w spaces or whatever that sequence is