K = int(input())
if K == 0:
    print(0)
else:
    E = [0.0] * K
    for x in range(K-1, -1, -1):
        total = 0.0
        for i in range(1, 7):
            next_x = x + i
            if next_x < K:
                total += E[next_x]
        E[x] = total / 6 + 1
    print("{0:.5f}".format(E[0]))