k=input()

eps=1e-2
l=0.0
r=1e9
p=[0]*(k+1)

while abs(l-r)>eps:
    c=(l+r)/2
    for i in range(1,k+1):
        p[i]= 1+sum([p[j] if j>=0 else c for j in range(i-6,i)])/6
    if p[k]>=c:
        l=c
    else:
        r=c

print (l+r)/2