#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
int main(){
    ll n;
    cin >> n;

    if(n <= 2)cout << -1 << '\n';
    else{
        cout << n*n*2 << '\n';
        vector<vector<ll>> pass(n*n,vector<ll>(0));

        for(ll i = 0; i < n*n; i++){
            pass[i].push_back((i+1)%(n*n));
            pass[i].push_back((n*n+i-1)%(n*n));
            pass[i].push_back((i+n)%(n*n));
            pass[i].push_back((n*n+i-n)%(n*n));

            sort(pass[i].begin(),pass[i].end());

            for(ll t = 0; t < 4; t++){
                if(i < pass[i][t]){
                    cout << i+1 << " " << pass[i][t]+1 << '\n';
                }
            }
        }
    }


    return 0;
}