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

int main() {
    int n;
    cin >> n;
    if(n <= 2){
        cout << -1 << endl;
    } else {
        cout << 2*n*n << endl;
        for(int i = 0; i < n*n; i++) {
            cout << i+1 << " " << (i+1)%(n*n) + 1 << " \n";
            cout << i+1 << " " << (i+n)%(n*n) + 1 << " \n";
        }
    }
    cout << "\n";
}