tema 5/17/2021

#include <iostream>
using namespace std;
#define NMAX 1'000
int n, arr[NMAX][NMAX];

void read() {
  cin >> n;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      cin >> arr[i][j];
    }
  }
}

void getSum() {
  int sum = 0;
  for (int i = 2; i < n; i++) {
    int j = n - 1;
    while (true) {
      if (i <= (n + 1) / 2) {
        if (j == n - i + 1) {
          break;
        }
      } else {
        if (i == j) {
          break;
        }
      }
      sum += arr[i][j];
      j--;
    }
  }
  cout << sum << endl;
}

int main() {
  read();
  getSum();
  return 0;
}