#include <bits/stdc++.h>
using namespace std;
vector<array<int, 2>> solve_case(int balls, vector<int> &arr) {
  vector<bool> alive(balls - 1, true);
  vector<array<int, 2>> answer(balls - 1);
  int cur = 0;
  for (int i = 0; i < balls - 1; i++) {
    map<int, vector<int>> cnt;
    int found = -1;
    while (true) {
      if (alive[arr[cur]]) {
        cnt[arr[cur]].push_back(cur);
        if (cnt[arr[cur]].size() > 1) {
          found = arr[cur];
          break;
        }
      }
      cur += 1;
    }
    assert(found + 1);
    answer[found][0] = cnt[found][0];
    answer[found][1] = cnt[found][1];
    alive[found] = false;
    cur += 1;
  }
  return answer;
}
void solve_single(int balls, vector<array<int, 2>> &arr, int offset,
                  vector<array<int, 2>> &answer) {
  vector<int> single(balls * (balls - 1));
  for (int i = 0; i < balls * (balls - 1); i++) {
    single[i] = arr[i][0];
  }
  vector<array<int, 2>> ans = solve_case(balls, single);
  for (int i = 0; i < balls - 1; i++) {
    answer[offset + i][0] = arr[ans[i][0]][1];
    answer[offset + i][1] = arr[ans[i][1]][1];
  }
}
int main() {
  int n, k;
  scanf("%d %d", &n, &k);
  int n_orig = n;
  vector<int> arr(n * k);
  for (int i = 0; i < n * k; i++) {
    scanf("%d", &arr[i]);
    arr[i] -= 1;
  }
  while (n % (k - 1) != 0) {
    for (int i = 0; i < k; i++) {
      arr.push_back(n);
    }
    n += 1;
  }
  int step = k - 1;
  vector<array<int, 2>> answer(n);
  for (int col = 0; col < n; col += step) {
    int col_start = col, col_end = col + step;
    vector<array<int, 2>> solve;
    for (int i = 0; i < n * k; i++) {
      if (col_start <= arr[i] && arr[i] < col_end) {
        solve.push_back({arr[i] - col_start, i});
      }
    }
    assert((int)solve.size() == k * (k - 1));
    solve_single(k, solve, col_start, answer);
  }
  for (int i = 0; i < n_orig; i++) {
    printf("%d %d\n", answer[i][0] + 1, answer[i][1] + 1);
  }
  return 0;
}
