// つら
#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define eb emplace_back
#define fast cin.tie(nullptr); ios_base::sync_with_stdio(false)
using namespace std;
using ll = long long;
using ull = unsigned long long;
constexpr ll mod = 998244353;

int n;
int f(int x){
    int m = n * n;
    for(int i = 1 ; i <= m; i++){
        if((x - i + m) % m == 0) return i;
    }
}
int main(){
    cin >> n;
    if(n <= 2){
        cout << -1 << endl;
        return 0;
    }
    int m = n * n;
    vector<vector<int>> g(m + 1);
    for(int i = 1; i <= m; i++){
        g[i].eb(f(i - 1));
        g[i].eb(f(i + 1));
        g[i].eb(f(i + n));
        g[i].eb(f(i - n));
    }
    cout << m * 2 << endl;
    for(int i = 1; i <= m; i++){
        for(auto to : g[i]){
            if(i < to)cout << i << " " << to << endl;
        }
    }
    return 0;
}