using System;

​

public class Program

    {

       public static void Main(string[] args)

        {

            Console.WriteLine("Enter a string to check if it's a palindrome:");

            string input = Console.ReadLine();

​

            if (IsPalindrome(input))

            {

                Console.WriteLine("The entered string is a palindrome.");

            }

            else

            {

                Console.WriteLine("The entered string is not a palindrome.");

            }

        }

​

        static bool IsPalindrome(string str)

        {

            str = str.ToLower();

​

            int left = 0;

            int right = str.Length - 1;

​

            while (left < right)

            {

                while (!char.IsLetterOrDigit(str[left]) && left < right)

                {

                    left++;

                }

                while (!char.IsLetterOrDigit(str[right]) && left < right)

                {

                    right--;

                }

​

                if (str[left] != str[right])

                {

                    return false;

                }

​

                left++;

                right--;

            }

​

            return true;

        }

    }

​

​