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 (Clang 3.8.0) (judge verdict: Accepted)

#include<stdio.h>
#include<string.h>
// Kaibun -> Yes +1 / No. -1
int kaibun (char *S, int N)
{
	for (int i = 0; i < (int)(N/2); i++)
      if (S [i] != S [N - 1 - i])
        return -1;
   	return 1;
}
int strongKaibun (char *S, int N)
{
  int Nprime = (N - 1) / 2;
  if (kaibun (S, N) == 1)
    if (kaibun (S, Nprime) == 1)
      if (kaibun (S + Nprime + 1, Nprime) == 1)
        return 1;
  return 0;
}
int main (void)
{
  char S [100];
  int N;
  scanf("%s", S);
  N = strlen (S); // N: oddは前提として暗黙に仮定してチェックしない。
  if (strongKaibun (S, N) == 1)
    printf ("Yes\n");
  else
    printf ("No\n");
  return 0;
}