import std.stdio, std.array, std.string, std.conv, std.algorithm; import std.typecons, std.range, std.random, std.math, std.container; import std.numeric, std.bigint, core.bitop, core.stdc.stdio; void main() { auto N = readln.chomp.to!int; auto P = readln.split.map!(x => x.to!real / 1000).array; auto Q = readln.split.map!(x => x.to!real / 100).array; auto pq = new BinaryHeap!(Array!(Tuple!(real, int)), "a < b"); foreach (i; 0..N) pq.insert(tuple(P[i] * Q[i], i)); real ans = 0; const int TRY = 10^^6; foreach (i; 1..TRY+1) { auto t = pq.front; ans += i * t[0]; pq.replaceFront(tuple(t[0] * (1 - Q[t[1]]), t[1])); } writefln("%.9f", ans); }