#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
using namespace std;

int main() {
    
    int n;cin>>n;
    vector<double> a(n-1);
    for(int i=0;i<n-1;i++) cin >> a[i];
    
    double dist = 1000;
    for(int i=0;i<n-1;i++){
        dist *= (1000-a[i])/1000;
    }
    
    cout << setprecision(15) << 1000 - dist << endl;
    
}