#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++){
		//05 14 23 32 41 50
		s = s + a[i][i];
		s = s + a[i][n-i-1];
	}
	
	cout<<s;
}

/**************************************************************
	Problem: 1726
	User: admin
	Language: C++
	Result: Accepted
	Time:27 ms
	Memory:2076 kb
****************************************************************/