3

using System;
using System.IO;
using System.Linq;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApp1
{


    class Program
    {

        static int BinToDec(string s, int k = 1)
        {
            if (s.Length > 0)
                return (s[s.Length - 1] - '0')*k + BinToDec(s.Substring(0, s.Length - 1), k * 2);
            return 0;
        }

        static void Main()
        {
            Console.Write("Enter binary number: ");
            string a = Console.ReadLine();
            Console.WriteLine("To dec : " + BinToDec(a));
        }
    }
}