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: Wrong Answer)

using System;

namespace AtCoder2020Ned
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = Console.ReadLine();
            var center = (input.Length - 1) / 2 + 1;

            if (!IsPalindrome(input.Substring(0, center - 1)))
            {
                Console.WriteLine("No");
                Console.Read();
                return;
            }

            if (!IsPalindrome(input.Substring(center, center - 1)))
            {
                Console.WriteLine("No");
                Console.Read();
                return;
            }

            Console.WriteLine("Yes");
            Console.Read();
        }

        static bool IsPalindrome (string str)
        {
            if (str.Length % 2 == 0)
            {
                return false;
            }

            var center = (str.Length - 1) / 2;
            var start = 0;
            var end = str.Length - 1;

            for (int i = 0; start != center; i++)
            {
                if (str[start] != str[end])
                {
                    return false;
                }
                else
                {
                    start++;
                    end--;
                    continue;
                }
            }

            return true;
        }
    }
}