#include <iostream>using namespace std;int N,a[101][101];void citire(){ cin>>N; for(int i=1;i<=N;i++) for(int j=1;j<=N;j++) cin>>a[i][j];}int S;void suma(){ for(int i=1;i<=N;i++) for(int j=1;j<=N;j++) if(i==j) S+=a[i][j+1]+a[i+1][j]; cout<<S;}int main(){ citire(); suma(); return 0;}