#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

int main()
{
    string s; cin >> s;
    
    int res = 0;
    for ( int i = 0; i < s.size(); i ++ )
    {
        int t = s[i] ^ 48;
        res += t;
    }
    cout << res;
    return 0;
}