#include<bits/stdc++.h>
using namespace std;
#define rep(i,n)for(int i=0;i<(int)(n);i++)
using ll=long long;
int main(){
    int n;
    cin>>n;
    int a[n],b[n],c[n];
    rep(i,n)cin>>a[i];
    rep(i,n)cin>>b[i];
    rep(i,n)c[i]=i;
    double d=0;
    do{
        int e=0;
        rep(i,n)if(a[i]>b[c[i]])e++;
        if(e>n/2)d++;
    }while(next_permutation(c,c+n));
    double nk=1;
    rep(i,n)nk*=i+1;
    cout<<fixed<<setprecision(5);
    cout<<d/nk<<endl;
}