#include <iostream>
#include <tuple>
#include <cmath>
#include <string>
#include <cstring>
#include <vector>
#include <deque>
#include <queue>
#include <stack>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <algorithm>
#include <vector>
#include <fstream>
#include <iomanip>
#include <ctime>
#include <cctype>
#include <climits>
#include <chrono>
#include <array>
 
using namespace std;
 
typedef long long ll;
typedef vector<int> vi;
typedef vector< vector <int> > vvi;
typedef pair<int, int> pii;
typedef pair < pair < int, int >, int > piii;
typedef pair < pair <int, int > , pair <int, int> > piiii;
typedef pair<ll, ll> pll;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<string> vs;
 
#define FOR(i,a,b) for(int i = a; i < b; i ++)
#define RFOR(i,a,b) for(int i = a-1; i >= b; i --)
#define all(a) a.begin(), a.end()
#define endl '\n';
#define sz(x) (int)(x).size()
 
#define mp make_pair
#define pb push_back
#define ff first
#define ss second
 
template <typename T>
void pr(vector<T> &v) {
    FOR(i, 0, sz(v)) cout << v[i] << " ";
    cout << endl;
}
template <typename T>
void pr(vector<vector<T> > &v) {
    FOR(i, 0, sz(v)) { pr(v[i]); }
}
template <typename T>
void re(T &x) {
    cin >> x;
}
template <typename T>
void re(vector<T> &a) {
    FOR(i, 0, sz(a)) re(a[i]);
}
template <class Arg, class... Args>
void re(Arg &first, Args &... rest) {
    re(first);
    re(rest...);
}
template <typename T>
void pr(T x) {
    cout << x << endl;
}
template <class Arg, class... Args>
void pr(const Arg &first, const Args &... rest) {
    cout << first << " ";
    pr(rest...);
    cout << endl;
}
void ps() { cout << endl; }
template<class T, class... Ts>
void ps(const T& t, const Ts&... ts) {
    cout << t; if (sizeof...(ts)) cout << " "; ps(ts...);
}
 
const ll MOD  = 998244353;
#define inf 1e18;
#define INF INT_MAX
 
long double PI = 4*atan(1);
long double eps = 1e-12;


long double pwin(long double p, long double a, long double b) {
    if(abs(p - 0.5) < 0.0001) {
        return b/(a+b);
    } else {
        if(p < 0.5) {
            long double x = pow(p/(1-p), a)-pow(p/(1-p), a+b);
            long double y = 1-pow(p/(1-p), a+b);
            return x/y;
        } else {
            long double x = pow((1-p)/p, b) - 1;
            long double y = pow((1-p)/p, a+b) - 1;
            return x/y;
        }
    }
    return 0.5;
}


int main() {
    //auto start = chrono::high_resolution_clock::now();
    ios_base::sync_with_stdio(0);cin.tie(0);
    //ofstream cout("output.txt");
    //ifstream cin("input.txt");
    #ifdef DEBUG
      freopen("input.txt", "r", stdin);
      freopen("output.txt", "w", stdout);
    #endif

    int n; cin >> n;
    vector<long double> p(n); re(p);

    vi tar(n+1); 
    FOR(i,0,n) cin >> tar[i+1];

    vector<long double> pup(1 << n);
    pup[0] = 1;

    for(int i = 1; i < (1 << n); i++) {
        int cnt = 0;
        for(int j = 0; j < n; j++) if(i & (1 << j)) cnt++;

        for(int j = 0; j < n; j++) {
            if(i & (1 << j)) {
                long double pos = pup[i ^ (1 << j)];
                long double up  = tar[cnt] - tar[cnt-1];
                long double down = tar[cnt] + tar[cnt-1];
                long double val = pos * pwin(p[j], up, down) + (1-pos) * pwin(p[j], down, up);
                pup[i] = max(pup[i], val);
            }
        }
    }


    cout << setprecision(12) << pup[(1 << n) - 1] << endl;

    
    
    //auto stop = chrono::high_resolution_clock::now();
    //auto duration = chrono::duration_cast<chrono::microseconds>(stop - start);
    //cout << duration.count() << endl;
    //cin.close();
    //cout.close();
}