def main():
    S = input()
    if len(S) % 2 == 1:
        print("NO")
        return

    S_first = S[:len(S)//2]
    S_second = S[len(S)//2:]

    if S_first == S_second:
        print("YES")
    else:
        print("NO")


if __name__ == "__main__":
    main()