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

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

double solve(int Border) {
	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++) {
			if (A[i + 1] > Border) {
				dp[i + 1][max(0, j - 1)] += dp[i][j] / 2.0;
				dp[i + 1][j] += dp[i][j] / 2.0;
			}
			else {
				dp[i + 1][j + 1] += dp[i][j] / 2.0;
				dp[i + 1][j] += dp[i][j] / 2.0;
			}
		}
	}

	double ret = 0;
	for (int i = 1; i <= N; i++) {
		if (A[i] <= Border) continue;
		ret += 1.0 * R[i] * dp[i - 1][0];
	}
	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];

	assert(1 <= N && N <= 500);
	for (int i = 1; i <= N; i++) assert(1 <= A[i] && A[i] <= 1000);
	for (int i = 1; i <= N; i++) assert(1 <= R[i] && R[i] <= 1000);

	// 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++) {
		if (vec[i].first == vec[i + 1].first) continue;
		double S1 = solve(vec[i].first);
		double S2 = 1.0 * (vec[i + 1].first - vec[i].first);
		Answer += S1 * S2;
	}
	printf("%.12lf\n", Answer * 1.0000001);
	return 0;
}