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: //package com.company.cf.global15;
  
  import java.io.BufferedReader;
  import java.io.File;
  import java.io.FileNotFoundException;
  import java.io.FileReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Comparator;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.NavigableSet;
  import java.util.StringTokenizer;
  import java.util.TreeSet;
  
  public class E {
      FastScanner in;
      PrintWriter out;
  
      private static final long MOD = 998244353;
  
      private final int[][] r = new int[50001][5];
  
      public static void main(String[] args) {
          new E().solve();
      }
  
      private void solve() {
          in = new FastScanner(System.in);
          out = new PrintWriter(System.out);
  
          solveCase();
  
          out.close();
      }
  
      private void solveCase() {
          int n = in.nextInt();
          int k = in.nextInt();
  
          int[] c = new int[n*k];
          for (int i = 0; i < n * k; i++) {
              c[i] = in.nextInt();
          }
  
          int in = 0;
          boolean[] alreadyRanged = new boolean[128];
          Arrays.fill(alreadyRanged, false);
          int[] last = new int[128];
          List<Range> ranges = new ArrayList<>();
          while (in < n) {
              Arrays.fill(last, -1);
  
              for (int i = 0; i < c.length; i++) if (!alreadyRanged[c[i]]) {
                  if (last[c[i]] == -1) {
                      last[c[i]] = i;
                  } else {
                      in++;
                      alreadyRanged[c[i]] = true;
                      ranges.add(new Range(last[c[i]], i));
                      Arrays.fill(last, -1);
                  }
              }
          }
  
          ranges.sort(Comparator.comparingInt(r -> c[r.a]));
  
          for (Range range : ranges) {
              out.print(range.a + 1);
              out.print(" ");
              out.print(range.b + 1);
              out.println();
          }
      }
  
      static class FastScanner {
  
          BufferedReader br;
          StringTokenizer st;
  
          public FastScanner(File f) {
              try {
                  br = new BufferedReader(new FileReader(f));
              } catch (FileNotFoundException e) {
                  e.printStackTrace();
              }
          }
  
          public FastScanner(InputStream f) {
              br = new BufferedReader(new InputStreamReader(f));
          }
  
          String next() {
              while (st == null || !st.hasMoreTokens()) {
                  String s = null;
                  try {
                      s = br.readLine();
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
                  if (s == null)
                      return null;
                  st = new StringTokenizer(s);
              }
              return st.nextToken();
          }
  
          boolean hasMoreTokens() {
              while (st == null || !st.hasMoreTokens()) {
                  String s = null;
                  try {
                      s = br.readLine();
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
                  if (s == null)
                      return false;
                  st = new StringTokenizer(s);
              }
              return true;
          }
  
          int nextInt() {
              return Integer.parseInt(next());
          }
  
          long nextLong() {
              return Long.parseLong(next());
          }
  
          double nextDouble() {
              return Double.parseDouble(next());
          }
      }
  
      private static class Range {
          public final int a;
          public final int b;
  
          public Range(int a, int b) {
              this.a = a;
              this.b = b;
          }
      }
  }
  