#include <bits/stdc++.h>

using namespace std;

#define DEBUG(x) cout <<'>'<<#x<<':'<< endl;
#define ll long long
#define vvi vector<vector<long long> >
#define vi vector<int>
#define INT 1000000000

int main(int argc, char** argv) {

    ios_base::sync_with_stdio(false);

    int N, M;

    while (cin >> N >> M) {
        
            vector<vector<long long> > orch(N, vector<ll>(N, 0));
            vvi ld(N + 2, vector<ll>(N + 2, 0));
            vvi lu(N + 2, vector<ll>(N + 2, 0));
            vvi rd(N + 2, vector<ll>(N + 2, 0));
            vvi ru(N + 2, vector<ll>(N + 2, 0));
            int x, y;
            for (int i = 0; i < M; i++) {
                cin >> x >> y;
                orch[x][y] = 1;
            }
            if (M % 2 == 1) {cout << -1 << endl; continue;}
            M /= 2;
            long long res = N * N;
            for (long long i = 1; i <= N; i++) {
                for (long long j = 1; j <= N; j++) {
    //                cout << i << " " << j << endl;
                    lu[i][j] = lu[i - 1][j] + lu[i][j - 1] - lu[i - 1][j - 1] + orch[i - 1][j - 1];
    //                cout << lu[i][j] << endl;
                    ru[i][N + 1 - j] = ru[i - 1][N + 1 - j] + ru[i][N - j + 2] - ru[i - 1][N - j + 2] + orch[i - 1][N - j];
    //                cout << ru[i][N + 1 - j] << endl;
                    ld[N - i + 1][j] = ld[N - i + 2][j] + ld[N - i + 1][j - 1] - ld[N - i + 2][j - 1] + orch[N - i][j - 1];
                    rd[N - i + 1][N - j + 1] = rd[N - i + 2][N - j + 1] + rd[N - i + 1][N - j + 2] - rd[N - i + 2][N - j + 2] + orch[N - i][N - j];

                    if (lu[i][j] >= M || ld[N - i + 1][j] >= M || ru[i][N + 1 - j] >= M || rd[N - i + 1][N - j + 1] >= M) {
    //                                    cout << lu[i][j] << endl;
    //                                    cout << ru[i][N + 1 - j] << endl;
    //                    cout << i << " " << j << endl;
    //                    cout << N - i + 1 << " " << j << endl;
    //                    cout << i << " " << N -j + 1 << endl;
    //                    cout << N - i + 1 << " " << N - j + 1 << endl;
                        res = min(res, i * j);
                    }
                }
            }
            cout << res << endl;

    }
    return 0;
}