import java.util.*;

public class Q133 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        Integer[] a = new Integer[N];
        Integer[] b = new Integer[N];
        for (int i = 0; i < N; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < N; i++) {
            b[i] = sc.nextInt();
        }

        Integer[] na = new Integer[N];
        Integer[] nb = new Integer[N];
        for (int i = 0; i < N; i++) {
            na[i] = i;
            nb[i] = i;
        }

        int cnt = 0;
        int win = 0;

        do {
            do {
                int awin = 0;
                int bwin = 0;
                for (int i = 0; i < N; i++) {
                    if (a[na[i]] > b[nb[i]]) awin++;
                    if (b[nb[i]] > a[na[i]]) bwin++;
                }
                if (awin > bwin) win++;
                cnt++;
            } while ((nb = (Integer[]) nextPermutation(nb)) != null);

            nb = new Integer[N];
            for (int i = 0; i < N; i++) {
                nb[i] = i;
            }
        } while ((na = (Integer[]) nextPermutation(na)) != null);

        System.out.println(1.0 * win / cnt);
    }

    private static Comparable[] nextPermutation(final Comparable[] c) {
        int first = _getFirst(c);
        if (first == -1) return null;

        int toSwap = c.length - 1;
        while (c[first].compareTo(c[toSwap]) >= 0) {
            toSwap--;
        }

        swap(c, first++, toSwap);

        toSwap = c.length - 1;
        while (first < toSwap) {
            swap(c, first++, toSwap--);
        }

        return c;
    }

    private static void swap(final Comparable[] c, final int i, final int j) {
        final Comparable tmp = c[i];
        c[i] = c[j];
        c[j] = tmp;
    }

    private static int _getFirst(final Comparable[] c) {
        for (int i = c.length - 2; i >= 0; i--) {
            if (c[i].compareTo(c[i + 1]) < 0) {
                return i;
            }
        }

        return -1;
    }
}