/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.06.05 21:21:43
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    string s;cin >> s;
    int ans = 0;
    for (int i = 1; i < s.size(); i++) {
        if (s[i] != '0') ans++;
    }
    cout << ans << endl;
    return 0;
}