import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]

def main():
    n = int(input())
    k = int(input())
    dp1 = [[0] * (n * 6 + 1) for _ in range(n + 1)]
    dp2 = [[0] * (n * 6 + 1) for _ in range(n + 1)]
    dp1[0][0] = dp2[0][0] = 1
    for i in range(n):
        s = 0
        for j in range(1, n * 6 + 1):
            s += dp2[i][j - 1]
            if j - 7 >= 0: s -= dp2[i][j - 7]
            dp2[i + 1][j] = s
    for i in range(k):
        s = 0
        for j in range(4, n * 6 + 1):
            s += dp1[i][j - 4] * 2
            if j - 7 >= 0: s -= dp1[i][j - 7] * 2
            dp1[i + 1][j] = s
    for i in range(k, n):
        s = 0
        for j in range(1, n * 6 + 1):
            s += dp1[i][j - 1]
            if j - 7 >= 0: s -= dp1[i][j - 7]
            dp1[i + 1][j] = s
    win=0
    s=0
    for j in range(1,n*6+1):
        s+=dp2[n][j-1]
        win+=dp1[n][j]*s
    print(win/pow(6,2*n))

main()