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# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;



class Program
{
    const int MOD = 1000000007;
    const int INF = 1 << 30;



    static void Main(string[] args)
    {
        Solve();
    }

    static void Solve()
    {
        Scaner sc = new Scaner();
        write wr = new write();
        Math2 mmath = new Math2();
        //ここから

        var x=sc.IntArr;
        var N=x[0];
        var A=sc.IntArr;

        double ans=0;
        for(int i=0;i<N;++i){
            ans+=1.0/(double)A[i];

        }

        wr.wri(1.0/ans);
        //ここまで
       
    }


    
}


 class Math2
{
    public long[] Fact;  //Nまでの階乗
    public long[] invFact;  //階乗の逆元
    public void FactoricalModSet(long N,long MOD=1000000007)
    {
        Fact = new long[N + 1];
        invFact = new long[N + 1];

        Fact[0] = 1;
        for(long i = 1; i <= N; ++i)
        {
            Fact[i] = Fact[i - 1] * i%MOD;
        }
        invFact[N] = powMOD(Fact[N], MOD - 2);

        for (long i = N; i > 0; --i)
        {
            invFact[i - 1] = invFact[i] * i%MOD;
        }

    }

    public long nCrMod(long n,long r,long MOD=1000000007)
    {
        return (Fact[n] * invFact[r] % MOD * invFact[n-r]%MOD);
    }

    public long powMOD(long x,long n,long MOD = 1000000007)
    {
        long res = 1;
        while (n > 0)
        {
            if ((n & 1) != 0) res = res * x % MOD;
            x = x * x % MOD;
            n >>= 1;
        }
        return res;
    }

    static long GCD(long x, long y)
    {
        if (y == 0) return x;
        return GCD(y, x % y);
    }

    static long LCM(long x, long y)
    {
        return x * y / GCD(x, y);
    }
}


class Scaner
{
    public string Str => Console.ReadLine();

    public string[] StrArr => Str.Split(' ');

    public long[] LongArr => StrArr.Select(long.Parse).ToArray();
    public int[] IntArr => StrArr.Select(int.Parse).ToArray();
    public char[] CharArr => Str.ToArray();
    public long Long1 => LongArr[0];
    public int Int1 => IntArr[0];
    
}



class write
{
    public  void wri<T>(T x)
    {
        Console.WriteLine(x);
    }
}