#include <bits/stdc++.h>
using namespace std;
const int N = 1010;
int a[N][N], n;
long long sum = 0;
int main(){
cin >> n;
for(int i = 1; i <= n; i ++ ){
for(int j = 1; j <= n; j ++ ){
cin >> a[i][j];
if(i == 1 && j == n) continue;
if(i == 1 && j == 1) continue;
if(i == n && j == 1) continue;
if(i == n && j == n) continue;
sum += a[i][j];
}
}
cout << sum;
return 0;
}
