//No.133 カードゲーム

import java.util.*;
import java.io.*;
import static java.util.Arrays.*;
import static java.lang.Math.*;

public class No133 {
    
    static final Scanner in = new Scanner(System.in);
    static final PrintWriter out = new PrintWriter(System.out,false);

    static void solve() {
        int n = in.nextInt();
        int[] a = new int[n];
        int[] b = new int[n];
        for (int i=0; i<n; i++) a[i] = in.nextInt();
        for (int i=0; i<n; i++) b[i] = in.nextInt();
        int win = 0,game = 0;
        sort(a);
        do {
            int cnt = 0;
            for (int i=0; i<n; i++) {
                if (a[i] - b[i] > 0) cnt++;
            }
            if (cnt > n/2) win++;
            game++;
        }while(nextPermutation(a));
        out.println((double)win/game);
    }

    static boolean nextPermutation(int[] a) {
        int n = a.length, i, j;
        for (i=n-2; i>=0 && a[i]>=a[i+1]; i--);
        if (i == -1) return false;
        for (j=i+1; j<n && a[i]<a[j]; j++);
        int temp = a[i]; a[i] = a[j-1]; a[j-1] = temp;
        for (int l=i+1, r=n-1; l<r; l++,r--) {
            temp = a[l]; a[l] = a[r]; a[r] = temp;
        }
        return true;
    }

    public static void main(String[] args) {
        long start = System.currentTimeMillis();

        solve();
        out.flush();

        long end = System.currentTimeMillis();
        //trace(end-start + "ms");
        in.close();
        out.close();
    }

    static void trace(Object... o) { System.out.println(deepToString(o));}
}