#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T, class U> using Pa = pair<T, U>;
template <class T> using vec = vector<T>;
template <class T> using vvec = vector<vec<T>>;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    string S;
    cin >> S;
    int ans = 0;
    for(int i=1;i<S.size();i++) if(S[i]!='0') ans++;
    cout << ans << "\n";
}