import sys
input=lambda: sys.stdin.readline().rstrip()
n=int(input())
k=int(input())
T=[0]*(6*n+1)
T[0]=1
for i in range(n):
  for j in range(6*n+1)[::-1]:
    T[j]=0
    for t in range(6):
      if j-t-1>=0:
        T[j]+=T[j-t-1]

TT=[0]*(6*n+1)
for i in range(6*n):
  TT[i+1]=TT[i]+T[i+1]

J=[0]*(6*n+1)
J[0]=1
for i in range(n):
  if i>=k:
    for j in range(6*n+1)[::-1]:
      J[j]=0
      for t in range(6):
        if j-t-1>=0:
          J[j]+=J[j-t-1]
  else:
    for j in range(6*n+1)[::-1]:
      J[j]=0
      for t in range(3,6):
        if j-t-1>=0:
          J[j]+=J[j-t-1]*2
ans=0
for i in range(2,6*n+1):
  ans+=J[i]*TT[i-1]
print(ans/pow(6,2*n))