#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

// https://codeforces.com/contest/1542/problem/D
int main() {
  int n; cin >> n;
  vector<int> a(n), r(n);
  REP(i, n) cin >> a[i];
  REP(i, n) cin >> r[i];
  double ans = 0;
  REP(i, n) {
    vector<double> dp(n, 0);
    dp[0] = 1;
    REP(j, i) {
      if (a[j] <= a[i]) {
        assert(dp[n - 1] < EPS);
        for (int k = n - 1; k > 0; --k) dp[k] = dp[k - 1];
        dp[0] = 0;
      }
      vector<double> nx(n, 0);
      REP(k, n) nx[k] = dp[k] / 2;
      nx[0] += dp[0] / 2;
      FOR(k, 1, n) nx[k - 1] += dp[k] / 2;
      dp.swap(nx);
    }
    FOR(j, i, n) {
      if (j > i && a[j] < a[i]) {
        assert(dp[n - 1] < EPS);
        for (int k = n - 1; k > 0; --k) dp[k] = dp[k - 1];
        dp[0] = 0;
      }
      vector<double> nx(n, 0);
      REP(k, n) nx[k] = dp[k] / 2;
      ans += dp[0] / 2 * a[i] * r[j];
      FOR(k, 1, n) nx[k - 1] += dp[k] / 2;
      dp.swap(nx);
    }
  }
  cout << ans << '\n';
  return 0;
}