#include <iostream>

using namespace std;

int main()

{

double sum = 0, mas[3][3];

for (int j = 0; j < 3; j++)

for (int jj = 0; jj < 3; jj++)

{

cin >> mas[j][jj];

if (j == jj)

sum += mas[j][jj];

};

cout<<"\n"<<sum;

}