#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using vll = vector<ll>;
using vvl = vector<vll>;
using pll = pair<ll,ll>;
#define rep(i,N) for(ll i=0;i<N;++i)
#define rrep(i,N) for(ll i=N-1; i>=0; --i)
#define all(v) (v).begin(), (v).end()

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    ll N,K;cin >> N >> K;
    vll P(N);
    rep(i,N){
        cin >> P[i];
        --P[i];
    }
    ll j;
    //入れ替えるのがmodK
    rep(i,N){//
        if(P[i]%K!=i%K){
            cout << "-1\n";
            return 0;
        }
    }
    vector<pll> bubble;//どことどこを{x,y}
    bool swapped;
    rep(r,K){
        swapped=true;
        while(swapped){
            swapped=false;
            for(ll i=r;i<N-K;++i){
                if(P[i]>P[i+K]){
                    swap(P[i],P[i+K]);
                    bubble.push_back({i+1,i+K+1});//1_indexed
                    swapped = true;
                }
            }
        }
    }
    cout << bubble.size() << endl;
    for(auto ans : bubble){
        cout << ans.first << " " << ans.second << endl;
    }
    return 0;
}