#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<ll>;
#define ov4(a, b, c, d, name, ...) name
#define rep3(i, a, b, c) for(ll i = (a); i < (b); i += (c))
#define rep2(i, a, b) rep3(i, a, b, 1)
#define rep1(i, n) rep2(i, 0, n)
#define rep0(n) rep1(aaaaa, n)
#define rep(...) ov4(__VA_ARGS__, rep3, rep2, rep1, rep0)(__VA_ARGS__)
#define per(i, a, b) for(ll i = (a)-1; i >= (b); i--)
#define fore(e, v) for(auto&& e : v)
#define all(a) begin(a), end(a)
#define si(a) (int)(size(a))
#define lb(v, x) (lower_bound(all(v), x) - begin(v))
#define eb emplace_back

template<typename T, typename S> bool chmin(T& a, const S& b) { return a > b ? a = b, 1 : 0; }
template<typename T, typename S> bool chmax(T& a, const S& b) { return a < b ? a = b, 1 : 0; }

const int INF = 1e9 + 100;
const ll INFL = 3e18 + 100;

#define i128 __int128_t

int main() { 
    cin.tie(0)->sync_with_stdio(0);
    ll n;
    cin >> n;
    if(n <= 2){
        cout << -1 << endl;
        return 0;
    }
    vector<pii> edge;
    ll r = n * n * 10000;
    ll w = n;
    rep(i,n){
        rep(j,n){
            ll idx = i * n + j;
            {
                ll x = i+1;
                ll y = j+0;
                ll jdx = (x * w + y + r) % (n * n);
                edge.emplace_back(idx+1,jdx+1);
            }
            {
                ll x = i+0;
                ll y = j+1;
                ll jdx = (x * w + y + r) % (n * n);
                edge.emplace_back(idx+1,jdx+1);
            }
        }
    }
    cout << edge.size() << endl;
    for(auto [u,v]:edge){
        cout << u << ' ' << v << endl;
    }
}