import java.lang.*;
import java.io.*;

public class BinaryToDecimal{
	public static void main(String[] args) throws IOException{
		BufferedReader bf= new BufferedReader(new InputStreamReader(System.in));
		System.out.print("Enter the Binary value: ");
		String str = bf.readLine();
		long num = Long.parseLong(str);
		long rem;
		while(num > 0){
			rem = num % 10;
			num = num / 10;
			if(rem != 0 && rem != 1){
				System.out.println("This is not a binary number.");
				System.out.println("Please try once again.");
				System.exit(0);
			}
		}
		int i= Integer.parseInt(str,2);
		System.out.println("Decimal:="+ i);
	}
}