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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Scanner;
import java.util.TreeMap;
class Main{


	static final int MOD = 1000000007;


	static ArrayList<ArrayList<Pair>> map;
	static TreeMap<Integer,Integer> ans; 
	static int maxnum;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);			//文字の入力
		int n = sc.nextInt();

		int[] a = new int[n];
		double sum = 0;
		for(int i = 0;i < n;i++){
			sum += 1/sc.nextDouble();
		}
		System.out.println(1/sum);
		
		

	}





	static int upperbond(int k,int min,int[] data){		//kより小さい最大の値をdataの中から探し、返す二分探索
		int max = data.length;
		//		if(min == data.length-1){
		//			if(data[min] > k){
		//				return min;
		//			}
		//		}

		while(max-min > 1){
			int mid = (max+min)/2;
			if(data[mid] >= k){
				max = mid;
			}else{
				min = mid;
			}
		}

		return max;
	}

	static int lowerbond(int k,int min,int[] data){		//kより大きい最小の値をdataの中から探し、返す二分探索
		int max = data.length;

		while(max-min > 1){
			int mid = (max+min)/2;
			if(data[mid] >= k){
				max = mid;
			}else{
				min = mid;
			}
		}
		return min;
	}



	static int gcd(int a,int b){				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}
	static long gcd(long a,long b){
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}



	static long lcm (long a, long b) {
		long g = gcd(a,b);
		return a/g*b;
	}




}

class Town{
	int index;
	int x ;
	int y;
	public Town(int index,int x,int y) {
		this.index = index;
		this.x = x;
		this.y = y;
		// TODO 自動生成されたコンストラクター・スタブ
	}


}


class Edge  implements Comparable{

	int index;
	HashSet<Integer> hen;
	HashSet<Integer> used;
	HashMap<Integer, Integer> map;
	int size;


	public Edge(int index) {
		// TODO 自動生成されたコンストラクター・スタブ
		this.index = index;
		hen = new HashSet();
		used = new HashSet<Integer>();
		map = new HashMap<Integer,Integer>();
	}

	public int compareTo(Object other) {
		Edge otherpair = (Edge)other;

		return   otherpair.hen.size() - hen.size();
	}
}

class Food implements Comparable{

	int minits;
	int score;
	double cospa;

	public Food(int from,int end,double c) {
		this.minits = from;
		this.score = end;
		this.cospa = c;
		// TODO 自動生成されたコンストラクター・スタブ
	}

	@Override
	public int compareTo(Object other) {
		Food otherpair = (Food)other;
		int dif = Double.compare(otherpair.cospa, cospa);
		return   dif;
	}

}

class Pair implements Comparable{
	int from;
	int end;
	public Pair(int from,int end) {
		this.from = from;
		this.end = end;
		// TODO 自動生成されたコンストラクター・スタブ
	}

	@Override
	public int compareTo(Object other) {
		Pair otherpair = (Pair)other;

		return  from - otherpair.from;
	}








}