package no210;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		double[] p = new double[n];
		double[] q = new double[n];
		for(int i=0;i<n;i++) {
			p[i] = sc.nextInt() / 1000D;
		}
		for(int i=0;i<n;i++) {
			q[i] = sc.nextInt() / 100D;
		}
		ArrayList<Double> al = new ArrayList<>();
		for(int i=0;i<n;i++) {
			for(int k=1;k<=100;k++) {
				al.add(p[i] * Math.pow(1-q[i], k-1) * q[i]);
			}
		}
		Collections.sort(al,Collections.reverseOrder());
		double e = 0;
		for(int i=0;i<al.size();i++) {
			e += (i+1) * al.get(i);
		}
		System.out.println(e);
	}

}