#coding: utf-8
##yuki_65


k=int(raw_input())

def f(x):
 if x>=k:
  return 0
 return 1.0+(f(x+1)+f(x+2)+f(x+3)+f(x+4)+f(x+5)+f(x+6))/6.0

print "%.5f" % f(0)