#include <bits/stdc++.h>

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