#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const long double PI = 4 * atan((long double)1);
long long power(long long a, long long n) {
  long long res = 1;
  while (n) {
    if (n % 2) res *= a;
    a *= a;
    n /= 2;
  }
  return res;
}
string bits(long long int n) {
  long long int m = n;
  string s;
  while (m != 0) {
    char x = (m % 2) + '0';
    s = s + x;
    m = m / 2;
  }
  reverse(s.begin(), s.end());
  return s;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  string s;
  cin >> s;
  int e = 0;
  long long int ans = 0;
  for (int i = s.size() - 1; i > 0; i--) {
    if (s[i] == '1') {
      if (e == 0) {
        ans += 2;
        e = 1;
      } else
        ans += 1;
    } else {
      if (e == 0)
        ans += 1;
      else
        ans += 2;
    }
  }
  if (e == 1) ans += 1;
  cout << ans;
  return 0;
}
