n = int(input())
k = int(input())

max_sum = 6 * n

# Calculate Jiro's probability distribution (normal dice)
jiro_dp = [0.0] * (max_sum + 1)
jiro_dp[0] = 1.0
for _ in range(n):
    next_dp = [0.0] * (max_sum + 1)
    for s in range(max_sum + 1):
        if jiro_dp[s] == 0:
            continue
        prob = jiro_dp[s] / 6
        for d in range(1, 7):
            next_sum = s + d
            if next_sum > max_sum:
                continue
            next_dp[next_sum] += prob
    jiro_dp = next_dp

# Calculate Taro's probability distribution (K loaded and N-K normal dice)
taro_dp = [0.0] * (max_sum + 1)
taro_dp[0] = 1.0

# Process K loaded dice
for _ in range(k):
    next_taro = [0.0] * (max_sum + 1)
    for s in range(max_sum + 1):
        if taro_dp[s] == 0:
            continue
        prob = taro_dp[s] / 3
        for d in [4, 5, 6]:
            next_sum = s + d
            if next_sum > max_sum:
                continue
            next_taro[next_sum] += prob
    taro_dp = next_taro

# Process N-K normal dice
for _ in range(n - k):
    next_taro = [0.0] * (max_sum + 1)
    for s in range(max_sum + 1):
        if taro_dp[s] == 0:
            continue
        prob = taro_dp[s] / 6
        for d in range(1, 7):
            next_sum = s + d
            if next_sum > max_sum:
                continue
            next_taro[next_sum] += prob
    taro_dp = next_taro

# Calculate the total winning probability
total = 0.0
for s in range(max_sum + 1):
    prob_taro = taro_dp[s]
    if prob_taro == 0:
        continue
    # Sum of Jiro's probabilities where his sum is less than s
    prob_jiro_less = sum(jiro_dp[:s])
    total += prob_taro * prob_jiro_less

# Print the result with five decimal places
print("{0:.5f}".format(total))