Problem:
Score : 200 points

Problem Statement

A string S of an odd length is said to be a strong palindrome if and only if all of the following conditions are satisfied:

S is a palindrome.

Let N be the length of S. The string formed by the 1-st through ((N-1)/2)-th characters of S is a palindrome.

The string consisting of the (N+3)/2-st through N-th characters of S is a palindrome.

Determine whether S is a strong palindrome.

Constraints

S consists of lowercase English letters.

The length of S is an odd number between 3 and 99 (inclusive).

Input

Input is given from Standard Input in the following format:

S

Output

If S is a strong palindrome, print Yes;
otherwise, print No.

Sample Input 1

akasaka

Sample Output 1

Yes

S is akasaka.

The string formed by the 1-st through the 3-rd characters is aka.

The string formed by the 5-th through the 7-th characters is aka.
All of these are palindromes, so S is a strong palindrome.

Sample Input 2

level

Sample Output 2

No

Sample Input 3

atcoder

Sample Output 3

No

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System.Collections.Generic;
using System.Linq;

public class Hello
{
    public static void Main()
    {
        hoge();
        System.Console.ReadLine();
    }

    public static void hoge()
    {
        var s = System.Console.ReadLine();
        var s1 = s.Substring(0, (s.Length - 1) / 2);
        var s2 = s.Substring(((s.Length + 3) / 2) - 1);

        s2 = new string(s2.Reverse().ToArray());

        if (!isk(s1))
        {
            System.Console.WriteLine("No");
            return;
        }

        System.Console.WriteLine(s1 == s2 ? "Yes" : "No");
    }

    public static bool isk(string s)
    {
        for(int i = 0; i < s.Length; i++)
        {
            if (s[i] != s[s.Length - i - 1])
            {
                return false;
            }
        }
        return true;
    }

}