#include <iostream>
#include <vector>
using namespace std;
typedef long long int64;
vector<int> a;
vector<int> b;
vector<bool> fa;
vector<bool> fb;
int n;

int64 process(int w, int ni)
{
    if(ni == 0)
    {
        if(w > n / 2)
            return 1;
        return 0;    
    }
    int64 res = 0;
    int bw = w;
    for(int i = 0; i < n; i++)
    {
        if(fa[i])
            continue;
        fa[i] = true;
        for(int j = 0; j < n; j++)
        {
            if(fb[j])
                continue;
            if(a[i] > b[j])
                w++;
            fb[j] = true;
            res += process(w, ni - 1);
            fb[j] = false;
            w = bw;
        }
        fa[i] = false;
    }
    return res;
}

int main(void)
{
    cin >> n;
    a.resize(n);
    b.resize(n);
    fa.resize(n, 0);
    fb.resize(n, 0);
    for(int i = 0; i < n; i++)
        cin >> a[i];
    for(int i = 0; i < n; i++)
        cin >> b[i];
    int64 p = 1;
    for(int i = 1; i <= n; i++)
        p *= i;
    cout << (double)process(0, n) / (p * p) << endl;
    return 0;
}