#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
#define all(a) a.begin(), a.end()
#define sz(a) ((int)a.size())
#define pb push_back
#ifdef Doludu
template <typename T>
ostream& operator << (ostream &o, vector<T> vec) {
    o << "{"; int f = 0;
    for (T i : vec) o << (f++ ? " " : "") << i;
    return o << "}";
}
void bug__(int c, auto ...a) {
    cerr << "\e[1;" << c << "m";
    (..., (cerr << a << " "));
    cerr << "\e[0m" << endl;
}
#define bug_(c, x...) bug__(c, __LINE__, "[" + string(#x) + "]", x)
#define bug(x...) bug_(32, x)
#define bugv(x...) bug_(36, vector(x))
#define safe bug_(33, "safe")
#else
#define bug(x...) void(0)
#define bugv(x...) void(0)
#define safe void(0)
#endif
const int mod = 998244353, N = 200087;

int add(int a, int b) { a += b; if (a >= mod) a -= mod; return a; }
int sub(int a, int b) { a -= b; if (a < 0) a += mod; return a; }
int mul(int a, int b) { return 1ll * a * b % mod; }
int Pow(int a, int b) { int ans = 1; for (; b; b >>= 1, a = mul(a, a)) if (b & 1) ans = mul(ans, a); return ans; }


int main() {
    ios::sync_with_stdio(false), cin.tie(0);
    int n;
    cin >> n;
    if (n == 2) {
        cout << "-1\n";
    } else {
        cout << n * n * 2 << "\n";
        for (int i = 0; i < n * n; ++i) {
            cout << i + 1 << " " << (i + n) % (n * n) + 1 << "\n";
            cout << i + 1 << " " << (i + 1) % (n * n) + 1 << "\n";
        }
    }
}