#include <iostream>
#include <iomanip>
using namespace std;
int main(void){
    int n;
    cin >> n;
    double a;
    double pos = 1000.0f;
    for (int i = 0; i < n-1; i++) {
        cin >> a;
        pos = pos * (1000.0f-a)/1000.0f;
    }
    cout << fixed << setprecision(26) << 1000 - pos << endl;
}