#!/usr/bin/env pypy
# -*- coding: utf-8 -*-

import random

EXP_TIMES = 500000


def jiro_dice(n):
    for i in range(n):
        yield random.randint(1, 6)


def taro_dice(n, k):
    for i in range(k):
        yield random.randint(4, 6)
    for j in range(n - k):
        yield random.randint(1, 6)


def conduct_experiment(n, k):
    taro = sum(taro_dice(n, k))
    jiro = sum(jiro_dice(n))
    if taro > jiro:
        return 1.0
    else:
        return 0.0


def main(times=EXP_TIMES):
    n = int(input())
    k = int(input())
    ans = sum(conduct_experiment(n, k) for x in range(times)) / float(times)
    print("{ans:.5f}".format(ans=ans))

if __name__ == "__main__":
    main()