import java.util.Scanner;

class Main {
    static int n;
    static int[] b;
    static int[] a;
    static long win = 0;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        a = new int[n];
        b = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        boolean used[] = new boolean[n];
        int[] tmp = new int[n];
        long battlenum[] = new long[n + 10];
        battlenum[0] = 1;
        battlenum[1] = 1;
        for (int i = 2; i < 10; i++) {
            battlenum[i] = i * battlenum[i - 1];
        }
        permutation(a, tmp, used, 0);
        System.out.println(win * 1.0 / battlenum[n]);

        sc.close();
    }

    public static void permutation(int[] origin, int[] tmp, boolean[] used, int index) {
        if (index == n) {
            // 処理
            Battle(tmp);
            return;
        }
        for (int i = 0; i < n; i++) {
            if (used[i])
                continue;
            tmp[index] = origin[i];
            used[i] = true;
            permutation(origin, tmp, used, index + 1);
            used[i] = false;
        }
    }

    public static void Battle(int[] op) {
        int cnt = 0;
        for (int i = 0; i < n; i++) {
            if (op[i] > b[i]) {
                cnt++;
            }
        }
        if (cnt > n / 2) {
            win++;
        }
    }
}