Problem:
Score : 200 points

Problem Statement

Given is a sequence of N integers A_1, \ldots, A_N.

Find the (multiplicative) inverse of the sum of the inverses of these numbers, \frac{1}{\frac{1}{A_1} + \ldots + \frac{1}{A_N}}.

Constraints

1 \leq N \leq 100

1 \leq A_i \leq 1000

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 \ldots A_N

Output

Print a decimal number (or an integer) representing the value of \frac{1}{\frac{1}{A_1} + \ldots + \frac{1}{A_N}}.

Your output will be judged correct when its absolute or relative error from the judge's output is at most 10^{-5}.

Sample Input 1

2
10 30

Sample Output 1

7.5

\frac{1}{\frac{1}{10} + \frac{1}{30}} = \frac{1}{\frac{4}{30}} = \frac{30}{4} = 7.5.

Printing 7.50001, 7.49999, and so on will also be accepted.

Sample Input 2

3
200 200 200

Sample Output 2

66.66666666666667

\frac{1}{\frac{1}{200} + \frac{1}{200} + \frac{1}{200}} = \frac{1}{\frac{3}{200}} = \frac{200}{3} = 66.6666....

Printing 6.66666e+1 and so on will also be accepted.

Sample Input 3

1
1000

Sample Output 3

1000

\frac{1}{\frac{1}{1000}} = 1000.

Printing +1000.0 and so on will also be accepted.

Solution in C++14 (Clang 3.8.0) (judge verdict: Accepted)

//
// Created by kuroneko on 2019-09-07.
//

#include <iostream>
#include <vector>
#include <cmath>
#include <iomanip>

using namespace std;

typedef long long ll;

#define INF 1000000000000009LL
#define MOD 1000000007LL

typedef int Weight;
struct Edge {
    int src, dst;
    Weight weight;
    Edge(int src, int dst, Weight weight):src(src), dst(dst), weight(weight) {}
};

typedef vector<Edge> Edges;
typedef vector<Edges> Graph;

typedef vector<Weight> Array;
typedef vector<Array> Matrix;

int main() {
    std::cout << std::fixed;
    std::cout << std::setprecision(10);
    int N; cin >> N;
    vector<ll> v(N);
    ll mul = 1;
    for (int i = 0; i < N; i++) {
        cin >> v[i];
    }

    double low = 0;
    for (int i = 0; i < N; i++) {
        low += 1.0 / v[i];
    }
    cout << 1.0 / low << endl;
    return 0;
}