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

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

    int N; cin >> N;
    if(N <= 2){cout << "-1\n"; return 0;}
    int n = N*N;
    cout << n*2 << "\n";
    for(int i=0; i<n; i++){
        int one = (i-1+n)%n,two = (i+1)%n,three = (i-N+n)%n,four = (i+N)%n;
        if(one < i) cout << one+1 << " " << i+1 << "\n";
        if(two < i) cout << two+1 << " " << i+1 << "\n";
        if(three < i) cout << three+1 << " " << i+1 << "\n";
        if(four < i) cout << four+1 << " " << i+1 << "\n";
    }
}