def main():
    n, k = int(input()), int(input())

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

    for i in range(1, n+1):
        for j in range(i, 6*i+1):
            for l in range(1, 7):
                if l <= j:
                    dp[i][j] += dp[i-1][j-l]

    dp2 = [[0 for j in range(6*n+1)] for i in range(k+1)]
    dp2[0][0] = 1

    for i in range(1, k+1):
        for j in range(4*i, 6*i+1):
            for l in range(4, 7):
                if l <= j:
                    dp2[i][j] += dp2[i-1][j-l]

    dp3 = [0] * (6*n+1)
    for i in range(6*n+1):
        for j in range(i+1):
            dp3[i] += dp[n-k][j] * dp2[k][i-j]

    comp, win = sum(dp[n]) * sum(dp3), 0
    for i in range(6*n+1):
        for j in range(i):
            win += dp3[i] * dp[n][j]

    print(win/comp)


if __name__ == '__main__':
    main()