#include <bits/stdc++.h>
using namespace std;
int main() {
  int n = 0;
  string s;
  for (int i = 0; i < s.size(); i++) {
    if (s[i] == '0') {
      n = n + 1;
    } else {
      n = n + 0;
    }
  }
  cout << n;
}
