import itertools

N=int(input())
A=list(map(int,input().split()))
B=list(map(int,input().split()))

casesA=itertools.permutations(A)
casesB=itertools.permutations(B)

ans=0
al=0
for a in casesA:
    for b in casesB:
        al+=1
        wa=0
        for ca,cb in zip(a,b):
            if ca>cb: wa+=1
        if wa>N//2: ans+=1

ans/=al
print(ans)