#include<stdio.h>
#include<string.h>
int main()
{
int m, n, j, k,sum=0;
int a[10][10];
for (m = 0; m <3; m++)
{
for (n = 0; n < 3; n++)
{
scanf("%d", &a[m][n]);
}
}
for (m = 0; m < 3; m++)
{
for (n = 0; n < 3; n++)
{
if (m + n == 2)
{
sum += a[m][n];
}
}
}
printf("%d", sum);
return 0;
}