#include <bits/stdc++.h>
using namespace std;
   
int a[20][20],n,s;
int i,j;
int main() {
    cin>>n;
    for(i = 0;i < n;i++){
        for(j = 0;j < n;j++){
            cin>>a[i][j];
        }
    }
       
    for(i = 0;i < n;i++){
        s = s + a[i][i];
        s = s + a[i][n-i-1];
    }
       
    cout<<s;
}
/**************************************************************
	Problem: 1726
	User: wuyichen
	Language: C++
	Result: Accepted
	Time:26 ms
	Memory:2076 kb
****************************************************************/