#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n - 1; i >= 0; --i)
#define FOR(i, m, n) for (int i = m; i < n; ++i)
#define FORR(i, m, n) for (int i = m; i >= n; --i)
#define ALL(v) (v).begin(),(v).end()
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
const ll INF=1LL<<60;
const int inf=(1<<30)-1;
const int mod=1e9;
int dx[8]={1,0,-1,0,-1,-1,1,1};
int dy[8]={0,1,0,-1,-1,1,-1,1};
int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;cin >> n;
    vector<int> a(n),b(n);
    REP(i,n) cin >> a[i];
    REP(i,n) cin >> b[i];
    vector<int> pa(n),pb(n);
    iota(ALL(pa),0);
    iota(ALL(pb),0);
    vector<double> fac(n+1);
    fac[0]=1;
    FOR(i,1,n+1) fac[i]=fac[i-1]*(double)i;
    double res=0;
    do{
        do{
            int cnt=0;
            REP(i,n) if(a[pa[i]]>b[pb[i]]) cnt++;
            if(cnt*2>n) res++;
        }while(next_permutation(ALL(pb)));
    }while(next_permutation(ALL(pa)));
    cout << fixed << setprecision(10) << res/fac[n]/fac[n] << endl;
}