module main;
// https://mayokoex.hatenablog.com/entry/2015/05/16/092914 より
// 確率
import std;

void main()
{
	// 入力
	int N = readln.chomp.to!int;
	auto P = readln.split.to!(double[]).map!((ref n) => n /= 1000).array;
	auto Q = readln.split.to!(double[]).map!((ref n) => n /= 100).array;
	// 答えの計算
	double ret = 0;
	alias T = Tuple!(double, int);
	auto que = iota(0, N).map!(i => T(P[i] * Q[i], i)).array.heapify;

	foreach (i; 1 .. 1_000_000) {
		T now = que.front;
		que.removeFront;

		ret += now[0] * i;
		que.insert(T(now[0] * (1 - Q[now[1]]), now[1]));
	}
	// 答えの出力
	writefln("%.12f", ret);
}