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

void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

int main() {
    fast_io();
    int n;
    cin >> n;
    double v = 1.0;
    for (int i = 1; i < n; i++) {
        int a;
        cin >> a;
        v *= (double)(1000 - a) / 1000;
    }
    cout << setprecision(16) << fixed << 1000 - 1000 * v << endl;
}