#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define all(s) (s).begin(), (s).end()
#define rall(s) (s).rbegin(), (s).rend()
#define rep(i,l,r) for(int i=l;i<r;i++)
#define rrep(i,r,l) for(int i=r;i>l;i--)

using ll=long long;
using mint=modint998244353;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N,K;cin>>N>>K;
    vector<int> P(N),idx(N);
    rep(i,0,N){
        cin>>P[i];
        idx[P[i]-1]=i;
    }
    vector<pair<int,int>> ans;
    rep(n,0,N){
        int pos=idx[n];
        if((pos-n)%K){
            cout<<-1<<endl;
            return 0;
        }
        while(pos>n){
            int a=P[pos-K]-1;
            swap(P[pos-K],P[pos]);
            swap(idx[n],idx[a]);
            ans.push_back({pos-K+1,pos+1});
            pos-=K;
        }
    }
    cout<<ans.size()<<endl;
    for(auto [a,b]:ans){
        cout<<a<<' '<<b<<'\n';
    }
}