#include<iostream>
#include<math.h>
using namespace std;
int main()
{
int n,b=0;
cout<<"enter a binary no. ";
cin>>n;
for(int i=0;n!=0;i++)
{if (n%10)
{b=b+pow(2,i);}
n=n/10;
}
cout<<b<<endl;
}
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