#include <iostream>
using namespace std;
int n, i, j, suma, num;
int main()
{
cout << "n= "; cin >> n;
cout << "introdu " << n << " linii cu "<< n << " elementele a tabloului bidimensional: \n";
for (i=0; i<n; ++i )
{
for (j=0; j<n; ++j)
{
cin >> num;
if (i>j && i+j<n-1)
suma=suma+num;
}
}
cout << suma;
}