#include <stdio.h>

void main(){
	int a[10][10];
	int i,n,j,x=0;
	scanf("%d",&n);

	for(i=0;i<n;i++){
		for(j=0;j<n;j++){
			scanf("%d",&a[i][j]);	
		}
	}

	for(i=0;i<n;i++){
		x=x+a[i][i]+a[i][n-i-1];
	}

	printf("%d",x);
}
/**************************************************************
	Problem: 1726
	User: admin
	Language: C
	Result: Accepted
	Time:31 ms
	Memory:1144 kb
****************************************************************/