#include <bits/stdc++.h>
#include <iostream>
#include <vector>
#include <algorithm>
#include <list> 
#include <atcoder/all>
using namespace std;

#define reps(i, a, n) for (int i = (a); i < (int)(n); ++i)
#define rep(i, n) reps(i, 0, n)

#define ALL(x) x.begin(),x.end() 
#define SIZE(x) ll(x.size()) 

#define INF32 2147483647 //2.147483647×10^{9}:32bit整数のinf
#define INF64 9223372036854775807 //9.223372036854775807×10^{18}:64bit整数のinf
#define MOD 1000000007 //問題による

#define F first
#define S second
#define ll long long

#define coutALL(x) for(auto i=x.begin();i!=--x.end();i++)cout<<*i<<" ";cout<<*--x.end()<<endl;
#define coutALL2d(vv) for(const auto& v : vv){for(const auto& e : v){cout << e << " ";}cout << endl;}

#define vi vector<int>
#define vvi vector<vector<int> >
#define vll vector<long long>
#define vvll vector<vector<long long> >

int main(){

int n;
cin >> n;
vector<double> a(n);
rep(i,n-1) cin >> a[i];

double x = 1;
rep(i,n-1){
    x = x * (1000-a[i])/1000;
}
x = x * 1000;
cout << std::setprecision(10)  <<1000-x << endl;
}