#include <bits/stdc++.h>
using namespace std;


int main(){
    int n;  cin >> n;
    vector<int> a(n - 1);
    for(auto& x : a){
        cin >> x;
    }

    double d = 1000.0, m = 1000.0;
    double ans = 0;
    for(auto& x : a){
        ans += x * (d / m);
		d = m - ans;
    }
    cout << setprecision(16) << ans << endl;

    return 0;
}