#include <bits/stdc++.h>   using namespace std;   const int maxn = 501;   long long matrix[maxn][maxn];   long long sum_col[maxn];   long long sum_row[maxn];   long long sum_d1 = 0;   long long sum_d2 = 0;   int pos_col = 0;   int pos_row = 0;   int main() {     int n, sum = 0;     cin >> n;     for (int i = 0; i < n; i++) {       for (int j = 0; j < n; j++) {         int tmp;         cin >> tmp;         if (tmp == 0) {           pos_col = j;           pos_row = i;         }         if (i == j) sum_d1 += tmp;         if (i == n - j - 1) sum_d2 += tmp;         sum_row[i] += tmp;         sum_col[j] += tmp;       }     }     if (n == 1) {       cout << 1;       return 0;     }     bool ans = true;     int cor = 0;     if (pos_col == cor) cor = 1;     long long num = sum_col[cor] - sum_col[pos_col];     if (num <= 0) ans = false;     sum_col[pos_col] += num;     sum_row[pos_row] += num;     if (pos_col == pos_row) sum_d1 += num;     if (pos_row == n - pos_col - 1) sum_d2 += num;     for (int i = 0; i < n; i++) {       if (sum_col[i] != sum_col[cor]) ans = false;       if (sum_row[i] != sum_col[cor]) ans = false;     }     if (sum_d1 != sum_col[cor]) ans = false;     if (sum_d2 != sum_col[cor]) ans = false;     if (ans)       cout << num;     else       cout << -1;   }   