def bitcount(N):
    ans=0
    while N!=0:
        ans+=1
        N&=N-1
    return ans

N,Pa,Pb=raw_input().split()
N=int(N)
Pa,Pb=float(Pa),float(Pb)
A=map(int,raw_input().split())
B=map(int,raw_input().split())
A.sort()
B.sort()
dpb=[[0.0 for i in range(N+1)] for j in range(N+1)]
dpmaskb=[0.0 for i in range(1<<N)]
dpmaskb[(1<<N)-1]=1.0
dpa=[[0.0 for i in range(N+1)] for j in range(N+1)]
dpmaska=[0.0 for i in range(1<<N)]
dpmaska[(1<<N)-1]=1.0
b=[bitcount(i) for i in range(1<<N)]

for i in range((1<<N)-1,-1,-1):
#    print "dpmaska[",i,"]=",dpmaska[i],
    for j in range(N):
        n=b[i]
        if (i&(1<<j))!=0:
            k=i-(1<<j)
            if k==(i&(i-1)):
                if n==1:
                    dpmaska[k]+=dpmaska[i]
                    dpmaskb[k]+=dpmaskb[i]
                    dpa[N-n][j]+=dpmaska[i]
                    dpb[N-n][j]+=dpmaskb[i]
                else: 
                    dpmaska[k]+=dpmaska[i]*Pa
                    dpmaskb[k]+=dpmaskb[i]*Pb
                    dpa[N-n][j]+=dpmaska[i]*Pa
                    dpb[N-n][j]+=dpmaskb[i]*Pb
            else:
                dpmaska[k]+=dpmaska[i]*(1.0-Pa)/(n-1)
                dpmaskb[k]+=dpmaskb[i]*(1.0-Pb)/(n-1)
                dpa[N-n][j]+=dpmaska[i]*(1.0-Pa)/(n-1)
                dpb[N-n][j]+=dpmaskb[i]*(1.0-Pb)/(n-1)
ans=0.0
for ai in range(N):
    for bi in range(N):
        if A[ai] > B[bi]:
            for ti in range(N):
                ans+=(A[ai]+B[bi])*dpa[ti][ai]*dpb[ti][bi]
print "%.11f"%ans