#include <iostream>
#include <vector>
using namespace std;
int n;
double niza[105];
double rec(int i, double result) {
    if(i == 0) {
        return result;
    }
    return rec(i - 1, 1.0 / (result + niza[i]));
}
int main()
{
    cin >> n;
    for(int i = 0; i < n; i++) {
        cin >> niza[i];
    }
    cout << rec(n - 1, 0.0) + niza[0] << endl;

    return 0;
}