using System;

public class Program

{

    public static void Main()

    {

        char[] input = "is this okay for you?        ".ToCharArray();

        Console.WriteLine(ReplaceString(input, 20));

    }

    // Given a string with enough spaces at the end and last index of input

    // replace all spaces with "%20"

    public static string ReplaceString(char[] str, int last)

    {

        int end = str.Length-1;

        while (last >=0 )

        {

            if (str[last] == ' ')

            {

                str[end--] = '0';

                str[end--] = '2';

                str[end--] = '%';

            }

            else

            {

                str[end--] = str[last];

            }

            last--;

        }

        return new string(str);

    }

}