#include <iostream>
using namespace std;
long n;
int  a[10000010], b[10000010];

int main() {
	long long sum = 0, sum1 = 0, sum2 = 0;
	double s;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> a[i];
		sum = sum + a[i];
	}
	sum = sum * 3;
	for (int i = 0; i < n; i++) {
		cin >> b[i];
		sum1 = sum1 + b[i];
	}
	sum1 = sum1 * 2;
	for (int i = 0; i < n; i++) {
		sum2 = sum2 + a[i] - b[i];
	}
	s = (sum - sum1) / sum2;
	printf("%.6lf", s);
	return 0;