k = input()

left = 0
right = 300
c = [0]*(k+1)
for t in xrange(90):
    mid = (left + right) / 2.
    for x in xrange(k-1,-1,-1):
        c[x] = sum(mid if x+i>k else c[x+i] for i in xrange(1,7))/6.+1
    if c[0]>mid:
        left = mid
    else:
        right = mid
print left