import random
import threading
from time import sleep


def solve():
    N = int(input())
    K = int(input())

    stop_event = threading.Event()

    def monte():
        w = g = 0
        while not stop_event.is_set():
            x = y = 0
            for j in range(N):
                if j < K:
                    x += random.randint(4, 6)
                else:
                    x += random.randint(1, 6)
                y += random.randint(1, 6)
            g += 1
            if x > y:
                w += 1
        print(w / g)

    threading.Thread(target=monte).start()

    sleep(4.8)
    stop_event.set()


if __name__ == '__main__':
    solve()