n=int(input())
kk=int(input())

dp = [[0]*(n*6+1) for _ in range(n+1)]
dp [0][0] = 1

dp2 = [[0]*(n*6+1) for _ in range(n+1)]
dp2[0][0] = 1

for i in range(n):
    for j in range(n*6+1):
        if dp[i][j] == 0:
            continue
        for k in range(1,7):
            if j+k < n*6+1:
                dp[i+1][j+k] += dp[i][j]
                
for i in range(n):
    for j in range(n*6+1):
        if dp[i][j] == 0:
            continue
        if i < n-kk:
            for k in range(1,7):
                if j + k < n*6+1:
                    dp2[i+1][j+k] += dp2[i][j]
                    
        else:
            for k in [4,4,5,5,6,6]:
                if j + k < n*6+1:
                    dp2[i+1][j+k] += dp2[i][j]
                    

bunbo=0
bunshi=0

for i in range(len(dp[-1])):
    for j in range(len(dp2[-1])):
        if i < j:
            bunshi += dp[-1][i]*dp2[-1][j]
        bunbo += dp[-1][i]*dp2[-1][j]
        

print(bunshi/bunbo)