#include<bits/stdc++.h>
using namespace std;

vector<pair<int,int>> bubble_sort(vector<int>A){
  vector<pair<int,int>> ret;
  int N=size(A);
  for(int i=0;i<N;i++){
    for(int j=0;j<N-i-1;j++) if(A[j]>A[j+1]){
      swap(A[j],A[j+1]);
      ret.emplace_back(j,j+1);
    }
  }
  return ret;
}

int main(){
  int N,K;cin>>N>>K;
  vector<int> P(N);
  for(auto&p:P)cin>>p;
  vector<pair<int,int>> ans;
  for(int i=0;i<K;i++){
    vector<int> Q;
    for(int j=i;j<N;j+=K) Q.emplace_back(P[j]);
    vector<pair<int,int>> op=bubble_sort(Q);
    for(auto&[a,b]:op)ans.emplace_back(a*K+i,b*K+i);
  }
  vector<int> sorted_P=P;
  ranges::sort(sorted_P);
  for(auto[a,b]:ans) swap(P[a],P[b]);
  if(P!=sorted_P){
    cout<<-1<<endl;
    return 0;
  }
  cout<<size(ans)<<endl;
  for(auto[a,b]:ans) cout<<a+1<<' '<<b+1<<endl;
}