# include<iostream> using namespace std; int a[101][101],n,h; int main(){ cin>>n; for(int i=0;i<n;i++) for(int j=0;j<n;j++){ cin>>a[i][j]; if(i==j) h+=a[i][j]; if(i+j==n-1) h+=a[i][j]; } if(n%2!=0) h-=a[n/2][n/2]; cout<<h; return 0; }