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

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

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

  int ans = 0;
  int n = s.size();
  for (int i = 1; i < n; i++) {
    if (s[i] == '0') continue;
    ans++;
  }
  cout << ans << endl;


}