N=int(input())
K=int(input())
dp0=[0]*(61)
dp0[0]=1
for _ in range(N):
    prev=dp0
    dp0=[0]*61
    for i in range(61):
        for j in range(1,7):
            if i+j<=60:
                dp0[i+j]+=prev[i]
dp1=[0]*(61)
dp1[0]=1
for _ in range(N-K):
    prev=dp1
    dp1=[0]*61
    for i in range(61):
        for j in range(1,7):
            if i+j<=60:
                dp1[i+j]+=prev[i]
for _ in range(K):
    prev=dp1
    dp1=[0]*61
    for i in range(61):
        for j in range(4,7):
            if i+j<=60:
                dp1[i+j]+=2*prev[i]
ans=0
for j in range(61):
    for i in range(j):
        ans+=dp0[i]*dp1[j]
ans/=6**(2*N)
print(ans)