#coding: utf-8
##yuki_75

f=[0.0 for i in xrange(202)]
g=[0.0 for i in xrange(202)]

k=int(raw_input())
f[k]=0.0
g[k]=0.0

for i in xrange(k-1,-1,-1):
 for j in xrange(1,7):
  if i+j<=k:
   f[i]+=(1.0/6)*f[i+j]
   g[i]+=(1.0/6)*g[i+j]
  else:
   f[i]+=1.0/6
 g[i]+=1.0

res=g[0]/(1.0-f[0])
print "%.4f" % res