# coding=utf-8
import random
N = int(input())
K = int(input())
result = [0, 0, 0]
NUM = 10 ** 5
table = [1] * K + [0] * (N-K)

random.seed()
for i in range(NUM):
    taro = 0
    jiro = 0
    for j in range(N):
        jiro += random.randrange(1, 6)
        if j < K:
            taro += random.randrange(4, 6)
        else:
            taro += random.randrange(1, 6)
    if taro > jiro:
        result[0] += 1
    if taro < jiro:
        result[1] += 1
    if taro == jiro:
        result[2] += 1
print(result[0]/NUM)