#include<bits/stdc++.h>
using namespace std;
int main()  
{
    string s;
    cin>>s;
    int r=0;
    int k=1;
    for(int i=s.size()-1;i>=0;i--)
    {
    	r=r+(s[i]-48)*k;
    	k=k*2;
	}
	cout<<r;
	return 0;
}
/**************************************************************
	Problem: 1290
	User: chenkexin
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2076 kb
****************************************************************/