#include <iostream>

using namespace std;

long long unsigned n,nr=1,num;

int main()
{
    cin>>n;

    while (n)
     {nr=nr*10+n%2;
     n/=10;}

   while (nr)
     {if ((nr%10)%2)
       num++;
      nr/=10;
     }
   cout<<num;
}