#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int N, A[5009], R[5009];
int cnt[5009];
double dp[5009][5009];
vector<pair<int, int>> vec;

double solve() {
	for (int i = 0; i <= N; i++) {
		for (int j = 0; j <= N; j++) dp[i][j] = 0;
	}
	dp[0][0] = 1.0;
	for (int i = 0; i < N; i++) {
		for (int j = 0; j <= N; j++) {
			dp[i + 1][j] += 0.5 * dp[i][j];
			dp[i + 1][min(j + 1, cnt[i + 1])] += 0.5 * dp[i][j];
		}
	}

	double ret = 0;
	for (int i = 1; i <= N; i++) {
		ret += 1.0 * R[i] * dp[i - 1][cnt[i]];
	}
	return ret / 2.0;
}

int main() {
	// Step #1. Input
	cin >> N;
	for (int i = 1; i <= N; i++) cin >> A[i];
	for (int i = 1; i <= N; i++) cin >> R[i];

	// Step #2. Sorting
	vec.push_back(make_pair(0, 0));
	for (int i = 1; i <= N; i++) vec.push_back(make_pair(A[i], i));
	sort(vec.begin(), vec.end());

	// Step #3. BruteForce
	double Answer = 0;
	for (int i = 0; i < N; i++) {
		for (int j = 0; j <= N; j++) cnt[j] = 0;
		for (int j = 0; j <= i; j++) {
			if (vec[j].second >= 1) cnt[vec[j].second] += 1;
		}
		for (int j = 1; j <= N; j++) cnt[j] += cnt[j - 1];

		double S1 = solve();
		double S2 = 1.0 * (vec[i + 1].first - vec[i].first);
		Answer += S1 * S2;
	}
	printf("%.12lf\n", Answer);
	return 0;
}