/* -*- coding: utf-8 -*-
 *
 * 884.cc:  No.884 Eat and Add - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 200000;

/* typedef */

/* global variables */

char s[MAX_N + 8];

/* subroutines */

/* main */

int main() {
  scanf("%s", s + 1);
  s[0] = '0';
  int n = strlen(s);
  //puts(s);

  int cnt = 0;
  for (int i = n - 1; i >= 0;) {
    while (i >= 0 && s[i] == '0') i--;
    if (i < 0) break;

    int j = i;
    while (s[j] == '1') j--;
    int l = i - j;

    if (l > 1) s[j] = '1';
    cnt++;
    i = j;
  }

  printf("%d\n", cnt);
  return 0;
}