#include <bits/stdc++.h>

int main() {
  using namespace std;
  cin.tie(nullptr)->sync_with_stdio(false);
  int n;
  cin >> n;
  vector<int> a(n), r(n);
  for (auto&& e : a) cin >> e;
  for (auto&& e : r) cin >> e;
  vector<int> order(n);
  iota(begin(order), end(order), 0);
  sort(begin(order), end(order), [&](int i, int j) { return a[i] < a[j]; });
  vector<bool> marked(n);
  vector p(n, vector<double>(n + 1));
  for (int k = 1; k <= n; ++k) {
    marked[order[k - 1]] = true;
    vector<double> f{1};
    for (int i = 0; i < n; ++i) {
      if (marked[i]) f.insert(begin(f), 0);
      p[i][k] = accumulate(begin(f) + 1, end(f), double(0));
      vector<double> nf(size(f));
      for (int x = 0; x < int(size(f)); ++x) {
        nf[x] += f[x] / 2;
        nf[max(x - 1, 0)] += f[x] / 2;
      }
      f = move(nf);
    }
  }
  double ans = 0;
  for (int i = 0; i < n; ++i)
    for (int k = 1; k <= n; ++k) ans += (p[i][k] - p[i][k - 1]) * a[order[k - 1]] * r[i];
  ans /= 2;
  cout.precision(10);
  cout << ans << '\n';
}