#include <iostream>
#include <string>
using namespace std;
string s;
int main(){
	cin >> s;
	s = "00" + s;
	int i,n = s.size();
	int dig = 0,ans = 0;
	for(i=n - 1;i>=1;i--){
		if(dig){
			if(s[i]=='1'){
				dig = 1;
				s[i] = '0';
			}else{
				dig = 0;
				s[i] = '1';
			}
		}
		if(s[i]=='1'){
			if(s[i - 1]=='0'){
				ans++;
				dig = 0;
			}else{
				s[i] = '0';
				if(dig==0){
					dig++; ans++;
				}
			}
		}
	}
	cout << ans << endl;
}