N = int(input())
K = int(input())


def roll(dice_getter):
    dp = [0] * (6 * N + 1)
    dp[0] = 1
    for i in range(N):
        dice = dice_getter(i)
        pp = [0] * (6 * N + 1)
        dp, pp = pp, dp
        for j in range(6 * N + 1):
            if pp[j] == 0: continue
            for d in dice:
                dp[j+d] += pp[j]

    return dp


fair_dice = [1, 2, 3, 4, 5, 6]
loaded_dice = [4, 4, 5, 5, 6, 6]
dice_sum1 = roll(lambda p: fair_dice)
dice_sum2 = roll(lambda p: fair_dice if p >= K else loaded_dice)

win = 0
tot = 0
for i in range(1, 6*N+1):
    for j in range(1, 6*N+1):
        tot += dice_sum1[i] * dice_sum2[j]
        if i < j:
            win += dice_sum1[i] * dice_sum2[j]

ans = win / tot
print(ans)