#include<bits/stdc++.h>
using namespace std;
int main(){
  int i,j,n,s=0;
  int a[100][100];
  cin>>n;
  for(i=0;i<n;i++)
  for(j=0;j<n;j++) cin>>a[i][j];
  for(i=0;i<n;i++){
  for(j=0;j<n;j++){
  if(i==j) s=s+a[i][j];
  if(i+j==n-1) s=s+a[i][j];
  }
  }
  cout<<s;
  return 0;
}

/**************************************************************
	Problem: 1726
	User: wtq001
	Language: C++
	Result: Accepted
	Time:28 ms
	Memory:2072 kb
****************************************************************/