#coding=UTF-8

N=int(input())
K=int(input())
#引き分けに注意
Tp=[1]
Jp=[1]

majime=[0]+[1]*6
ika=[0,0,0,0]+[2]*3
for idx in range(0,N,1):
    tmp=[0]*(len(Jp)-1+len(majime)-1+1)
    for idy in range(0,len(Jp),1):
        for idz in range(0,len(majime),1):
            tmp[idy+idz]+=Jp[idy]*majime[idz]
    Jp=tmp
#    print(Jp)

for idx in range(0,K,1):
    tmp=[0]*(len(Tp)-1+len(ika)-1+1)
    for idy in range(0,len(Tp),1):
        for idz in range(0,len(ika),1):
            tmp[idy+idz]+=Tp[idy]*ika[idz]
    Tp=tmp
for idx in range(0,N-K,1):
    tmp=[0]*(len(Tp)-1+len(ika)-1+1)
    for idy in range(0,len(Tp),1):
        for idz in range(0,len(ika),1):
            tmp[idy+idz]+=Tp[idy]*majime[idz]
    Tp=tmp
ans=0
for idx in range(0,len(Jp),1):
    for idy in range(idx+1,len(Tp),1):
        ans=ans+Tp[idy]*Jp[idx]

print(ans/(6**(2*N)))