import std.algorithm, std.conv, std.range, std.stdio, std.string;

void main()
{
  auto n = readln.chomp.to!size_t;
  auto pi = readln.split.to!(real[]).map!"a / 1000".array;
  auto qi = readln.split.to!(real[]).map!"a / 100".array;

  auto r = real(0), s = real(1);
  foreach (_; 0..100000) {
    auto i = n.iota.map!(j => pi[j] * qi[j]).maxIndex, p = pi[i], q = qi[i];
    foreach (j; 0..n) {
      if (i == j)
        pi[j] = p * (1 - q) / (1 - p * q);
      else
        pi[j] /= 1 - p * q;
    }

    r += (p * q + 1) * s;
    s *= (1 - p * q);
    if (s < 1e-9) break;
  }

  writefln("%.4f", r - 1);
}