# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	S = input()
	N = len(S)
	if N % 2 == 1:
		print("NO")
		return

	M = int(N // 2)
	a = S[:M]
	b = S[M:]
	if a == b:
		print("YES")
	else:
		print("NO")

if __name__ == '__main__':
	main()