N = int(input())
K = int(input())
M = 100
JDP = [0] * M
JDP[0] = 1
for _ in range(N):
    JDP2 = [0] * M
    for i in range(M):
        for k in range(1,7):
            if i - k >= 0:
                JDP2[i] += JDP[i-k]
    JDP = list(JDP2)
TDP = [0] * M
TDP[0] = 1
for _ in range(N-K):
    TDP2 = [0] * M
    for i in range(M):
        for k in range(1,7):
            if i - k >= 0:
                TDP2[i] += TDP[i-k]
    TDP = list(TDP2)
for _ in range(K):
    TDP2 = [0] * M
    for i in range(M):
        for k in range(4,7):
            if i - k >= 0:
                TDP2[i] += TDP[i-k] * 2
    TDP = list(TDP2)
W = 0
G = 0
for j in range(M):
    for t in range(M):
        if j < t:
            W += JDP[j] * TDP[t]
        G += JDP[j] * TDP[t]
print(W / G)