using System;
using System.Linq;
class Program {
    static void Main() {
        Console.Write("Enter string: ");
        string str = Console.ReadLine();
        string rev = new string(str.Reverse().ToArray());
        Console.WriteLine(str == rev ? "Palindrome" : "Not palindrome");
    }
}

or 

using System;
class Palindrome
{
    static void Main()
    {
        Console.Write("Enter a string: ");
        string str = Console.ReadLine();
        string rev = "";

        for (int i = str.Length - 1; i >= 0; i--)
            rev += str[i];

        if (str == rev)
            Console.WriteLine("Palindrome");
        else
            Console.WriteLine("Not Palindrome");
    }
}