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: Runtime Error)

using System;
using System.Linq;

class Program
{
    private static string S1;
    private static string S2;
    private static bool res = true;
    static void Main(string[] args)
    {
        string S = Console.ReadLine();
        int N = S.Length;
        S1 = S.Substring(0, (N - 1) / 2);
        S2 = S.Substring(((N + 3) / 2) - 1, N - ((N + 3) / 2) + 1);
        rec1(0, S1.Length - 1);
        if (res)
            rec2(0, S2.Length - 1);
        if (res)
            Console.WriteLine("Yes");
    }
    static void rec1(int a, int b)
    {
        if (a == b) return;
        if (S1[a] == S1[b])
            rec1(a + 1, b - 1);
        else
        {
            Console.WriteLine("No");
            res = false;
            return;
        }
    }
    static void rec2(int c, int d)
    {
        if (c == d) return;
        if (S2[c] == S2[d])
            rec2(c + 1, d - 1);
        else
        {
            Console.WriteLine("No");
            res = false;
            return;
        }
    }
}