import java.util.Scanner; import static java.lang.System.*; import java.util.ArrayList; public class Main { public static void main(String[] args) { Scanner scan = new Scanner(in); double n = scan.nextDouble(); double sumX = 0; double sumW = 0; ArrayList<Double> ws = new ArrayList<Double>(); for (double i = 0; i < n; ++i) { double w = scan.nextDouble(); ws.add(w); } for (double i = 0; i < n; ++i) { double x = scan.nextDouble(); sumX += x; sumW += ws.get((int)i) * x; } out.println(sumW / sumX); } }