#include <iostream>
#include <string>

using namespace std;

int main()
{
	int n,count = 0;
	char num;

	cin >> n;

	if(n < 1)
	{
		cout << 0 << endl;
		return 0;
	}
	for(int i = 0; i < n; i++)
	{
		for(int j = 0; j < n; j++)
		{
			cin >> num;
			if(j == n-1 - i || j == i)
			{
				count += num-48;
			}
		}
	}
	cout << count << endl;
	return 0;
}