using System;

using System.Text.RegularExpressions;

public class Program

{

    public static Regex re = new Regex(@"^(a+)[b-z]\1$");

    public static void Main()

    {

        check("aca");

        check("ada");

        check("aadaa");

        check("aaddaa");

        check("aadcaa");

        check("aaaaaaaadaa");

        check("aadaaaaaaaa");

    }

    public static void check(string str)

    {

        Console.WriteLine(str + " -> " + re.IsMatch(str));

    }

}