#include<iostream> using namespace std; int main(){ int n,a[101][101],k=1,sum=0; cin>>n; for(int i=1;i<=n;i++){ for(int j=1;j<=n;j++){ cin>>a[i][j]; if(i==j||i+j==n+1) sum+=a[i][j]; } } cout<<sum; return 0; }