N=int(raw_input())
K=int(raw_input())
Taro=[0 for i in range(61)]
Jiro=[0 for i in range(61)]
Taro[0]=1
Jiro[0]=1
for i in range(N):
    for j in range(60,-1,-1):
        Taro[j]=0
        Jiro[j]=0
        for k in range(1,7):
            if j-k >= 0:
                Jiro[j]+=Jiro[j-k]/6.0
        if i>=K:
            for k in range(1,7):
                if j-k >= 0:
                    Taro[j]+=Taro[j-k]/6.0
        else:
            for k in range(4,7):
                if j-k >= 0:
                    Taro[j]+=Taro[j-k]/3.0
prob=0
for i in range(61):
    for k in range(i+1,61):
        prob += Jiro[i]*Taro[k]
print prob