N = input()
K = input()
dp0 = [[0.0] * 100 for _ in range(20)]
dp1 = [[0.0] * 100 for _ in range(20)]
dp0[0][0] = dp1[0][0] = 1.0
for i in range(N):
    for j in range(70):
        for k in range(1, 7):
            dp0[i+1][j+k] += dp0[i][j] / 6.0
        if i < K:
            for k in range(4, 7):
                dp1[i+1][j+k] += dp1[i][j] / 3.0
        else:
            for k in range(1, 7):
                dp1[i+1][j+k] += dp1[i][j] / 6.0

ans = sum(dp1[N][i] * dp0[N][j] for i in range(N*6+1) for j in range(N*6+1)
          if i > j)
print('%.5f' % ans)