#include<iostream> using namespace std; int main(){ int n; double a[11][11],result=0; cin>>n; int n1=n-1,n2=n/2; for(int y=0;y<n;y++) for(int x=0;x<n;x++) cin>>a[y][x]; for(int i=0;i<n;i++) result+=a[i][i]+a[i][n1-i]; if(n%2!=0) result-=a[n2][n2]; cout<<result; return 0; }