#yuki_58
import random

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

res=0.0
r=3*10**6
for i in xrange(r):
 taro=jiro=0
 for i in xrange(n):
  jiro+=random.randint(1,6)
 for i in xrange(k):
  taro+=random.randint(4,6)
 for i in xrange(n-k):
  taro+=random.randint(1,6)
 if taro>jiro:
  res+=1
print 1.0*res/r