def main():
    n = input()

    if len(n) < 3:
        exit(print(0))

    if len(n) % 3 != 0:
        exit(print('9' * (len(n) // 3)))

    ans = 0
    i = 1
    while int(str(i) * 3) <= int(n):
        ans += 1
        i += 1

    print(ans)


if __name__ == "__main__":
    main()