#include <iostream>

using namespace std;

int main()
{
int a, sum = 0;
cin >> a;
for (int i = 1; i <= 13744; i++) {
    if (i % 2 == 0) {
        sum += a%10 ;
    }
    a /= 10;
    if (a == 0) {
        break;
    }
}
cout << sum;
return 0;
}