k = int(input())
e = [0] * (k + 10)
x = [0] * (k + 10)
for i in range(k + 1, k + 6):
    x[i] = 1
for i in range(k)[::-1]:
    a = b = 0
    for j in range(i + 1, i + 7):
        a += e[j]
        b += x[j]
    e[i] = a / 6 + 1
    x[i] = b / 6
ans = e[0] / (1 - x[0])
print(ans)