N = int(input())
p = [0] * (N+6)
for i in range(N-1, -1, -1):
    p[i] = p[i+1]/6 + p[i+2]/6 + p[i+3]/6 + p[i+4]/6 + p[i+5]/6 + p[i+6]/6 + 1
print(p[0])