#include <bits/stdc++.h>

using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
const int N = 2000010, MOD = 1e9 + 7, INF = 0x3f3f3f3f;
int n, m, w[N];



int main() {
    cin >> n;
    if (n <= 2) {
        puts("-1");
        return 0;
    }
    printf("%d\n", (n * n) << 1);
    for (int i = 1; i <= n * n; i++) {
        int a = i % n ? i + 1 : i - n + 1, b = i / n == n ? i % n : i + n;
        printf("%d %d\n%d %d\n", i, a, i, b);
    }
    return 0;
}