#include <bits/stdc++.h>
using namespace std;


int main() {
  string c;
  cin >> c;

  int ans = 0;
  int n = c.size();
  for (int i = 1; i < n; ++i) {
    if (c[i] != '0') ans++;
  }
  cout << ans << '\n';
  return 0;
}