#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using P = pair<int, int>;
using PL = pair<lint, lint>;
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
#define ALL(a)  (a).begin(),(a).end()
constexpr int MOD = 1000000007;
constexpr lint B1 = 1532834020;
constexpr lint M1 = 2147482409;
constexpr lint B2 = 1388622299;
constexpr lint M2 = 2147478017;
constexpr int INF = 2147483647;
void yes(bool expr) {cout << (expr ? "Yes" : "No") << "\n";}
template<class T>void chmax(T &a, const T &b) { if (a<b) a=b; }
template<class T>void chmin(T &a, const T &b) { if (b<a) a=b; }
int main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int N;
  cin >> N;
  vector<int> A(N);
  REP(i, N) cin >> A[i];
  vector<int> R(N);
  REP(i, N) cin >> R[i];
  double ans = 0;
  REP(i, N) {
    vector<vector<double>> dp(N+1, vector<double>(N+1));
    dp[0][0] = 1.0;
    REP(k, N) REP(l, N) {
      if(k > i && l == 0) continue;
      if(A[k] < A[i] || (A[k] == A[i] && k <= i)) {
        dp[k+1][l+1] += dp[k][l] * 0.5;
        dp[k+1][l] += dp[k][l] * 0.5;
      } else {
        dp[k+1][max(0, l-1)] += dp[k][l] * 0.5;
        dp[k+1][l] += dp[k][l] * 0.5;
      }
    }
    FOR(j, i, N) ans += dp[j+1][0] * A[i] * R[j];
  }
  cout << fixed << setprecision(10) << ans << "\n";
}