题解

#include <bits/stdc++.h>
using namespace std;
int main() {
	string s;
	cin >> s;
	int sum = 0;
	for (int i = s.size() - 1, j = 1; i >= 0; i--, j *= 2)
        sum += (s[i] - '0') * j;
	cout << sum;
	return 0;
}