using System;

public class Program

{

    public static void Main(){

        Console.WriteLine(validPalindrome("aabaa"));

    }

    public static bool validPalindrome(String input){

        if(input == null || input.Length == 0) return true;

        input = input.Replace("[^a-zA-Z0-9]", "").ToLower();

        int i = 0;

        int j = input.Length - 1;

        while(i < j){

            if(input[i] != input[j]){

                return false;

            }

            i++;

            j--;

        }

        return true;

    }

​

}