#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define REP(i,n) for(ll i=0;i<ll(n);i++)
#define REPE(i,l,n) for(ll i=l;i<=ll(n);i++)
#define FORA(i,I) for(const auto& i:I)

int main() {
    double n, tcnt = 0.0, gcnt = 0.0, twin = 0.0, gwin = 0.0;
    cin >> n;
    vector<ll> a(n), b(n);
    REP(i, n) cin >> a[i];
    REP(i, n) cin >> b[i];
    
    sort(b.begin(), b.end());
    do{
        sort(a.begin(), a.end());
        do{
            ++tcnt;
            gcnt = gwin = 0;
            REP(i, n){
                ++gcnt;
                if(a[i] > b[i]) ++gwin;
            }
            if(gwin * 2 > gcnt) ++twin;
        }while(next_permutation(a.begin(), a.end()));
    }while(next_permutation(b.begin(), b.end()));

    printf("%.7f\n", twin/tcnt);
}