using System;
public class Program
{
public static bool IsBinary(int N)
while (N!=0)
if (N%10>1)
return false;
N=N/10;
}
return true;
public static double DecNumber(int n)
int i=0,D;
double sum=0;
while (n!=0)
D=n%10;
n=n/10;
sum=sum+D*Math.Pow(2,i);
i++;
return sum;
public static void Main()
{int n;
Console.WriteLine("enter a binary number: ");
n=int.Parse(Console.ReadLine());
if (IsBinary(n))
Console.WriteLine(DecNumber(n));
else
Console.WriteLine("error");