#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 r,int c){
    return r * n + c + 1;
}
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 = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            int u = f(i, j);
            int v1 = f((2 * i) % n, (2 * j) % n);
            int v2 = f((2 * i) % n, (2 * j + 1) % n);
            int v3 = f((n - 2 + i) % n, (n - 2 + j) % n);
            int v4 = f((n - 1 + i) % n, (n - 1 + j) % n);
            g[u].eb(v1);
            g[u].eb(v2);
            g[u].eb(v3);
            g[u].eb(v4);
        }
    }
    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;

}