#include<stdio.h>
int main()
{
int N,i,j,sum=0;
scanf("%d",&N);
int M[N][N];
for(i=0;i<N;i++){
for(j=0;j<N;j++){
scanf("%d",&M[i][j]);
if(!(i+j==N-1||i==N-1||j==N-1)){
sum+=M[i][j];
}
}
}
printf("%d",sum);
}