#include<iostream>
#include<string>
#include<cmath>
using namespace std;
void binToDec(string getBinary);
int main()
{
	string getBinary;
	cout<<"Enter a Binary Number:"<<endl;
	cin>>getBinary;
	binToDec(getBinary);
 
return 0;
}
void binToDec(string getBinary)
{
	int setLength,total=0;
	double placeholder=0;
	setLength=getBinary.size();
 
	for(int i=setLength;i>0;i--)
	{
		int num=pow(2.0,placeholder);
		int test=getBinary[i];
		if (test==1)
		{
			total=total+num;
		}
 
		placeholder=placeholder +1;
 
	}
	cout<<total<<endl;
 
 
}