import std.conv, std.functional, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.numeric, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum NUM_ITERS = 10^^6;

int N;
real[] P, Q;

void main() {
  try {
    for (; ; ) {
      N = readInt();
      P = new real[N];
      foreach (i; 0 .. N) {
        P[i] = readReal() / 1000.0;
      }
      Q = new real[N];
      foreach (i; 0 .. N) {
        Q[i] = readReal() / 100.0;
      }
      
      auto q = BinaryHeap!(Array!(Tuple!(real, int)))();
      foreach (i; 0 .. N) {
        q.insert(tuple(P[i] * Q[i], i));
      }
      real ans = 0.0;
      real sum = 1.0;
      foreach (iter; 0 .. NUM_ITERS) {
        if (isSubnormal(sum)) {
          break;
        }
        real r = q.front[0];
        int i = q.front[1];
        q.removeFront;
        ans += sum;
        sum -= r;
        q.insert(tuple(r * (1.0 - Q[i]), i));
      }
      writefln("%.10f", ans);
    }
  } catch (EOFException e) {
  }
}