Decimal to Binary Num

//Using loops write a program that converts an integer number to its binary representation. The input is entered as long. The output should be a variable of type string. Do not use the built-in .NET functionality. Examples:
//decimal	    binary
//0	            0
//3	            11
//43691	        1010101010101011
//236476736	    1110000110000101100101000000

using System;
class DecimalToBinaryNum
{
    static void Main()
    {
        long input = long.Parse(Console.ReadLine());
        string binNum = "";
        string[] binArray = new string[50];

        for (int i = 0; input > 0; i++)
        {
            if (input == 1)
            {
                binNum = "1";
            }
            else
            {
                if (input % 2 == 0)
                {
                    binNum = "0";
                }
                else
                {
                    binNum = "1";
                }
            }
            input = input / 2;
            binArray[i] = binNum;
        }

        Array.Reverse(binArray);
        foreach (var decDigit in binArray)
        {
            Console.Write(decDigit);
        }
        Console.WriteLine();
    }
}