#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <stack>
#include <queue>
using namespace std;

main() {
    int n,k;
    cin>>n>>k;
    int p[n];
    for (int i=0;i<n;i++)
        cin>>p[i];

    vector <pair<int,int>> ans;
    for (int r=0;r<k;r++) {

        int z=0;
        while ((z*k)+r<n) z++;

        for (int a=0;a<z;a++) {
            int mn=a;
            for (int b=a+1;b<z;b++)
                if (p[b*k+r]<p[mn*k+r]) mn=b;

            if (mn==a) continue;

            ans.push_back(make_pair(a*k+r, mn*k+r));
            swap(p[a*k+r], p[mn*k+r]);
        }
    }

    bool yes=true;
    for (int i=1;i<n;i++)
        if (p[i]<=p[i-1]) yes=false;

    if (yes) {
        cout<<ans.size()<<endl;
        for (auto x : ans)
            cout<<x.first+1<<" "<<x.second+1<<endl;
    } else cout<<-1<<endl;
}