#include <bits/stdc++.h>
#define all(x) x.begin(),x.end()
#define long long long
#define INF 1000000001
#define LNF 10000000011000000001
using namespace std;

int main()
{
	ios_base::sync_with_stdio(0); 
    cin.tie(0);
    
    int n;
    cin >> n;
    int m = n*n;

    if(n < 3)
    {
        cout << -1 << endl;
        return 0;
    }
    cout << m*2 << "\n";

    for(int i = 1; i<=m; i++)
    {
        cout << i << " " << (((i+1) > m) ? i+1-m : i+1) << "\n";
        cout << i << " " << (((i+n) > m) ? i+n-m : i+n) << "\n";
    }
    return 0;
}