#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#define _USE_MATH_DEFINES
#include <cmath>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iostream>
#include <iterator>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;

#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

const int INF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007; // 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
/*-------------------------------------------------*/
int main() {
  cin.tie(nullptr); ios::sync_with_stdio(false);
  // freopen("input.txt", "r", stdin);

  string s; cin >> s;
  reverse(ALL(s));
  int n = s.length(), ans = 0, pos = s.find('1');
  while (pos < n) {
    int nx = s.find('0', pos);
    if (nx == s.npos) nx = n;
    int len = nx - pos;
    if (len >= 2 || (nx + 1 < n && s[nx + 1] == '1' && nx + 2 < n && s[nx + 2] == '1')) {
      ++ans;
      FOR(i, pos, nx) s[i] = '0';
      if (nx == n) {
        s += '1';
        ++n;
      } else {
        s[nx] = '1';
      }
      pos = nx;
    } else {
      ++ans;
      pos = nx;
      nx = s.find('1', pos);
      if (nx == s.npos) nx = n;
      pos = nx;
    }
  }
  cout << ans << '\n';
  return 0;
}