string = input()

length = len(string)

if length % 2 == 1:
    hikaku = False
else:
    hulf_length = int(length / 2)

    hikaku = True

    for str_idx in range(hulf_length):
        if string[str_idx] != string[str_idx + hulf_length]:
            hikaku = False

if hikaku:
    print('YES')
else:
    print('NO')