#include <bits/stdc++.h>
#pragma GCC target("avx2")
/*
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
*/
#pragma GCC target("prefer-vector-width=512")
#pragma GCC optimize("Ofast,unroll-loops")

using namespace std;
using i32 = int;
using i64 = long long;
using f32 = float;
using f64 = double;
using f80 = long double;

#define rep(i, n) for(i64 i = 0; i < (n); i++)
#define all(x) (x).begin(), (x).end()

template<class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << ", " << p.second << ")";
    return os;
}

template<class T>
istream& operator>>(istream& is, vector<T>& v) {
    for(int i = 0; i < (int)v.size(); i++) {
        is >> v[i];
    }
    return is;
}

template<class T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    for(int i = 0; i < (int)v.size(); i++) {
        if(i > 0) os << " ";
        os << v[i];
    }
    return os;
}

void YesNo(bool yn) {
    if(yn) cout << "Yes" << endl;
    else cout << "No" << endl;
}

void YesNoExit(bool yn) {
    YesNo(yn);
    exit(0);
}

template<class T, class U>
bool chmin(T &x, U y) {
    if(y < x) {
        x = y;
        return true;
    }
    return false;
}

template<class T, class U>
bool chmax(T &x, U y) {
    if(y > x) {
        x = y;
        return true;
    }
    return false;
}

struct UnionFind {
  vector<int> data;

  UnionFind() = default;

  explicit UnionFind(size_t sz) : data(sz, -1) {}

  bool unite(int x, int y) {
    x = find(x), y = find(y);
    if (x == y) return false;
    if (data[x] > data[y]) swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return true;
  }

  int find(int k) {
    if (data[k] < 0) return (k);
    return data[k] = find(data[k]);
  }

  int size(int k) { return -data[find(k)]; }

  bool same(int x, int y) { return find(x) == find(y); }

  vector<vector<int> > groups() {
    int n = (int)data.size();
    vector<vector<int> > ret(n);
    for (int i = 0; i < n; i++) {
      ret[find(i)].emplace_back(i);
    }
    ret.erase(remove_if(begin(ret), end(ret),
                        [&](const vector<int>& v) { return v.empty(); }),
              end(ret));
    return ret;
  }
};

void out() { cout << '\n'; }
template <class T, class... Ts>
void out(const T& a, const Ts&... b) {
    cout << a;
    (cout << ... << (cout << ' ', b));
    cout << '\n';
}

vector<i32> dx4 = {0, 1, 0, -1};
vector<i32> dy4 = {1, 0, -1, 0};
vector<i32> dx8 = {0, 1, 0, -1, 1, 1, -1, -1};
vector<i32> dy8 = {1, 0, -1, 0, 1, -1, 1, -1};

const i64 mod = 998244353;

void solve() {
    i32 n; cin >> n;
    i32 m = n * n;

    if(n == 2) {
        out(-1);
        return;
    }

    out(2 * m);
    rep(i, m) {
        out(i + 1, (i + n) % m + 1);
        out(i + 1, (i + 1) % m + 1);
    }
}

int main() {
    int TESTCASE = 1;
    // cin >> TESTCASE;
    while(TESTCASE--) {
        solve();
    }
}