#include <bits/stdc++.h>

int main() {
	std::string s;
	std::cin >> s;
	std::reverse(s.begin(), s.end());
	s.push_back('0');
	int n = s.size();
	int dp[n + 1][2];
	for (int i = 0; i <= n; i++) dp[i][0] = dp[i][1] = 1000000000;
	dp[0][0] = 0;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 2; j++) {
			if (s[i] == '0' && !j) dp[i + 1][0] = std::min(dp[i + 1][0], dp[i][j]);
			else if (s[i] == '1' && j) dp[i + 1][1] = std::min(dp[i + 1][1], dp[i][j]);
			else dp[i + 1][0] = std::min(dp[i + 1][0], dp[i][j] + 1), dp[i + 1][1] = std::min(dp[i + 1][1], dp[i][j] + 1);
		}
	}
	std::cout << dp[n][0] << std::endl;
	return 0;
}