What would be the value in sum of the following statements when executed?

int sum, k, i, j;

int x [4] [4] = {{1 , 2 , 3 , 4} , {5 , 6 , 7 , 8} , {9 , 8 , 7 , 3} , {2 , 1 ,7 , 1}};

sum = x [0] [0]

for ( int k=1 ; k<=3 ; ++k)

sum += x [k] [k];

I thank you for your help in advance.