#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 < 3)cout << -1 << '\n';
    else{
        cout << n * n * 2 << '\n';

        vector<vector<ll>> hen(n*n,vector<ll>(4,0));
        hen[0][0] = 2;
        hen[0][1] = 3;
        hen[0][2] = n*n-1;
        hen[0][3] = n*n;

        for(ll i = 1; i < n*n; i++){
            for(ll t = 0; t < 4; t++){
                hen[i][t] = hen[i-1][t] + 1;
                if(hen[i][t] > n*n)hen[i][t] = 1;
            }
            sort(hen[i].begin(),hen[i].end());
        }

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

        
    }

    return 0;
}