#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef long double ld;
typedef pair<int,int> P;

int main() {
  string s;
  cin >> s;
  s = '0' + s;
  reverse(s.begin(), s.end());
  int i = 0;
  int n  = s.size();
  int res = 0;
  for (int i = 0; i < n; i++) {
    if (s[i] == '1') {
      if (s[i + 1] == '0') {
        s[i] = '0';
        res++;
      } else {
        while (s[i] == '1') i++;
        s[i] = '1';
        i--;
        res++;
      }
    }
  }
  cout << res << endl;
  return 0;
}