# coding: utf-8
#yuki_58
import random

n=int(raw_input())
k=int(raw_input())

res=0
for i in xrange(800000):
 temp=0
 for j in xrange(n):
  temp+=random.randrange(1,7)
  if j<k:
   temp-=random.randrange(4,7)
  else:
   temp-=random.randrange(1,7)
 res+=(temp<0)

print 1.0*res/800000