N=int(input())
K=int(input())
dp1=[[0]*(6*N+1) for _ in range(N+1)]
dp2=[[0]*(6*N+1) for _ in range(N+1)]
dp1[0][0]=dp2[0][0]=1
for i in range(1,N+1):
    for j in range(6*N+1):
        if i<=K:
            for k in range(4,7):
                if j-k<0:continue
                dp1[i][j]+=dp1[i-1][j-k]*2
        else:
            for k in range(1,7):
                if j-k<0:continue
                dp1[i][j]+=dp1[i-1][j-k]
        for k in range(1,7):
            if j-k<0:continue
            dp2[i][j]+=dp2[i-1][j-k]
den=sum(dp1[N])*sum(dp2[N])
num=0
for i in range(6*N+1):
    for j in range(6*N+1):
        if i<=j:continue
        num+=dp1[N][i]*dp2[N][j]
print(num/den)