...

#include<bits/stdc++.h>
using namespace std;
int main() {
int n;
cin >> n;
int a[n][n];
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
cin >> a[i][j];
}
}
int sum = 0;
for (int i = 0; i < n; i++) {
sum = sum + a[i][i] + a[i][n - 1 - i];
}
if (n % 2 == 1) {
sum = sum - a[n / 2][n / 2];
}
cout << sum;
return 0;
}