using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Enter string to check if plaindrome:");

        string str = Console.ReadLine();

        Console.WriteLine("Is string {0} a plaindrome ?: {1}", str, IsPalindrome(str));

    }

    private static bool IsPalindrome(string str)

    {

        if(string.IsNullOrWhiteSpace(str)) return true;

        int len = str.Length;

        for(int start=0, end=len-1; start<=end; start++,end--)

        {    

            while(start < len && !Char.IsLetterOrDigit(str[start]))

            {

                start++;

            }

            while(end >= 0 && !Char.IsLetterOrDigit(str[end]))

            {

                end--;

            }

            if(start >= len || end < 0) return true;

            if(Char.ToLower(str[start]) != Char.ToLower(str[end]))

                return false;

        }

        return true;

    }

}