using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Enter String");

        var input = Console.ReadLine();

        var revstr = Rev(input);

        Console.WriteLine(revstr);

        if(input == revstr){

            Console.WriteLine(input + " is a palindrome.");

        } else {

            Console.WriteLine(input + " is not a palindrome.");

        }

        Console.WriteLine("\nWhich letter would you like to replace in " + input + "?");

        var c1 = Console.ReadLine();

        Console.WriteLine("\nWhich letter would you like to replace it with?");

        var c2 = Console.ReadLine();

        Console.WriteLine(Rep(input,c1,c2));

    }

    public static string Rev(string str){

        char[] strArr = str.ToCharArray();

        Array.Reverse(strArr);

        return new string(strArr); //Converts char array to string

    }

    public static string Rep(string s,string c1,string c2){

        s = s.Replace(c1, c2);

        return s;

    }

}