#include <bits/stdc++.h>
using namespace std;
int main(void){
    int n,k;
    cin>>n>>k;
    vector<int>a(n),b;
    for(int i=0;i<n;i++)cin>>a[i];
    b=a;
    vector<array<int,2>>ans;
    for(int i=0;i<k;i++){
        while(1){
            int flag=1;
            for(int j=i;j+k<n;j+=k){
                if(a[j]>a[j+k]){
                    swap(a[j],a[j+k]);
                    ans.push_back({j+1,j+k+1});
                    flag=0;
                }
            }
            if(flag)break;
        }
    }
    sort(b.begin(),b.end());
    if(a!=b){
        cout<<-1<<endl;
    }else{
        cout<<ans.size()<<endl;
        for(auto x:ans){
            cout<<x[0]<<" "<<x[1]<<endl;
        }
    }
    return 0;
}