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.Collections.Generic;
class Program
{
	static void Main(string[] args)
	{
		string str = Console.ReadLine();
		bool flag = true;
		int N = str.Length;
		for(var i=0;i<N;i++){
			if(str.Substring(i,1)!=str.Substring(N-1-i,1)){
				flag = false;
			}
		}
		for(var i=0;i<(N-1)/2;i++){
			if(str.Substring(i,1)!=str.Substring((N-1)/2-1-i,1)){
				flag = false;
			}
		}
		for(var i=(N-3)/2-1;i<N;i++){
			if(str.Substring(i,1)!=str.Substring(N-1-i,1)){
				flag = false;
			}
		}
		if(flag){
			Console.WriteLine("Yes");
		} else {
			Console.WriteLine("No");
		}
	}
}