#include <iostream>
using namespace std;
int main()
{
	int n,k;
	int nul=0;
	int sum = 0;
	cin >> n;
	for (int i =0; i<n*n; i++)
	{
		cin >> k;
		if (k==0)
		{
			nul++;
		}
		else
		{
			sum+=k;
		}		
	}
	n = n*n/2;
	if (nul<=n)
	{
		cout << sum;
	}
	else
	{
		cout << -1;
	}
}