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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.io.*;
// import java.math.*;
import java.util.*;
// import java.util.Map.*;
// import java.util.stream.*;

public class Main {
    public static void main (String[] args) throws IOException {
        FastScanner sc = new FastScanner();
        final int N = sc.nextInt();
        double[] A = sc.doubleArray (N);
        System.out.println (
            1 / Arrays.stream (A).reduce (0, (pre, cur) -> pre + 1 / cur));
        return;
    }

    // FastScanner start
    static class FastScanner {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;
        public FastScanner() {
            din = new DataInputStream (System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }
        public FastScanner (String file_name) throws IOException {
            din = new DataInputStream (new FileInputStream (file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }
        private byte read() throws IOException {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }
        public void close() throws IOException {
            if (din == null)
                return;
            din.close();
        }
        private void fillBuffer() throws IOException {
            bytesRead = din.read (buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }
        public char nextChar() throws IOException {
            byte c = read();
            while (Character.isWhitespace (c)) {
                c = read();
            }
            return (char)c;
        }
        public String nextString() throws IOException {
            byte c = read();
            while (Character.isWhitespace (c)) {
                c = read();
            }
            StringBuilder builder = new StringBuilder();
            builder.append ((char)c);
            c = read();
            while (!Character.isWhitespace (c)) {
                builder.append ((char)c);
                c = read();
            }
            return builder.toString();
        }
        public int nextInt() throws IOException {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }
        public long nextLong() throws IOException {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }
        public double nextDouble() throws IOException {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (c == '.') {
                while ((c = read()) >= '0' && c <= '9') {
                    ret += (c - '0') / (div *= 10);
                }
            }
            if (neg)
                return -ret;
            return ret;
        }
        public char[] charArray (int n) throws IOException {
            char arr[] = new char[n];
            for (int i = 0; i < n; i++)
                arr[i] = nextChar();
            return arr;
        }
        public String[] stringArray (int n) throws IOException {
            String arr[] = new String[n];
            for (int i = 0; i < n; i++)
                arr[i] = nextString();
            return arr;
        }
        public int[] intArray (int n) throws IOException {
            int arr[] = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextInt();
            }
            return arr;
        }
        public long[] longArray (int n) throws IOException {
            long arr[] = new long[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextLong();
            }
            return arr;
        }
        public double[] doubleArray (int n) throws IOException {
            double arr[] = new double[n];
            for (int i = 0; i < n; i++)
                arr[i] = nextDouble();
            return arr;
        }
    }
    // FastScanner end
}