sentence = input()
sentence_list = list(sentence)
num = len(sentence_list)

if num % 2 == 0:
    half = num // 2
    list1 = list()
    list2 = list()
    for i in range(half):
        list1 = sentence_list[i]
    for j in range(half):
        list2 = sentence_list[j + half]
    if list1 == list2:
        print("YES")
    else:
        print("NO")
else:
    print("NO")