#include <bits/stdc++.h>
#include <string>
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <deque>
#include <stack>
using namespace std;

int main()
{
	//freopen("input.txt", "r", stdin); /*freopen("output.txt","w",stdout);*/
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);
	int n;
	cin>>n;
	long long a,b;
	long long c;
	for(int i=0;i<n;i++)
	{
		cin>>c;
		if(i==0)
		{
			a=1;
			b=c;
		}
		else
		{
			a=a*c+b;
			b=b*c;
		}
		for(int ii=2;ii<=sqrt(min(a,b));ii++)
		{
			while(a%ii==0&&b%ii==0)
			{
				a/=ii;
				b/=ii;
			}
		}
	}
	cout<<fixed<<setprecision(15)<<(double)b/a;
	return 0;
}
