include iostream using namespace std int main int int nul int sum cin

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#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;
}
}