#include <bits/stdc++.h>
#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
#include <iomanip>
#include<set>
#include <numeric>
#include<string>
using ll = long long;
using namespace std;

int main()
{
    ll n;
    cin >> n;
    double v = 1;
    for (int i = 0; i < n - 1; i++){
        double t;
        cin >> t;
        v *= ((1000-t)/1000);
    }
    cout << fixed << setprecision(7);
    cout << 1000 * (1 - v) << endl;
}