#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
using namespace std;
using ll = long long;
string a;
ll ans;
int main() {
  cin >> a;
  rep(i,a.size()){
    if(a.at(i) != '0'){
      ++ans;
    }
  }
  cout << ans -1<< endl;
  return 0;
}