using System; public class Hello { public static void Main() { var s = Console.ReadLine().Trim(); Console.WriteLine(check(s) ? "YES" : "NO"); } public static bool check(string s) { var sL = s.Length; if (sL % 2 == 1) return false; var s1 = s.Substring(0, sL / 2); var s2 = s.Substring(sL / 2); return s1 == s2; } }