#include <iostream>
#include <cstring>
using namespace std;
typedef long long ll;
ll n, a[6], b[6], c[6], d[6];
double res;
bool e[6], f[6];

void dfs(ll x){
    if (x == n * 2) {
        ll A = 0, B = 0;
        for (ll i = 0; i < n; i++) {
            if (c[i] > d[i]) A++;
            if (c[i] < d[i]) B++;
        }
        if (A > B) res++;
    } else if (x < n) {
        for (ll i = 0; i < n; i++) {
            if (e[i]) continue;
            c[x] = a[i];
            e[i] = true;
            dfs(x + 1);
            e[i] = false;
        }
    } else {
        for (ll i = 0; i < n; i++) {
            if (f[i]) continue;
            d[x - n] = b[i];
            f[i] = true;
            dfs(x + 1);
            f[i] = false;
        }
    }
}

int main(void){
    // Your code here!
    cin >> n;
    for (ll i = 0; i < n; i++) cin >> a[i];
    for (ll i = 0; i < n; i++) cin >> b[i];
    dfs(0);
    for (ll i = 2; i <= n; i++) res /= i * i;
    cout << res << endl;
}