#include <iostream>

int main(){
	std::string S;
	std::cin >> S;
	long long ans = 0, onelength = 0;
	for(char c : S){
		if(c == '1'){
			onelength++;
			continue;
		}
		ans += onelength >>= 1;
		onelength <<= 1;
	}
	std::cout << ans << std::endl;
	return 0;
}