/* -*- coding: utf-8 -*-
 *
 * 3775.cc:  No.3775 Distant  Swap - yukicoder
 */

#include<cstdio>
#include<vector>
#include<algorithm>
#include<utility>

using namespace std;

/* constant */

const int MAX_N = 1000;

/* typedef */

using pii = pair<int,int>;
using vpii = vector<pii>;

/* global variables */

int ps[MAX_N], vs[MAX_N];

/* subroutines */

/* main */

int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  for (int i = 0; i < n; i++) scanf("%d", ps + i);

  vpii ops;
  for (int i = 0; i < k; i++) {
    int l = 0;
    for (int j = i; j < n; j += k) vs[l++] = j;

    for (int j = l - 1; j >= 1; j--)
      for (int j0 = 0; j0 < j; j0++) {
	int v0 = vs[j0], v1 = vs[j0 + 1];
	if (ps[v0] > ps[v1]) {
	  ops.push_back({v0, v1});
	  swap(ps[v0], ps[v1]);
	}
      }
  }

  bool ok = true;
  for (int i = 0; ok && i + 1 < n; i++) ok = (ps[i] < ps[i + 1]);

  if (ok) {
    printf("%d\n", (int)ops.size());
    for (auto [i, j]: ops) printf("%d %d\n", i + 1, j + 1);
  }
  else
    puts("-1");
  
  return 0;
}