Problem:
Score : 100 points

Problem Statement

Given is an integer N.

Takahashi chooses an integer a from the positive integers not greater than N with equal probability.

Find the probability that a is odd.

Constraints

1 \leq N \leq 100

Input

Input is given from Standard Input in the following format:

N

Output

Print the probability that a is odd.
Your output will be considered correct when its absolute or relative error from the judge's output is at most 10^{-6}.

Sample Input 1

4

Sample Output 1

0.5000000000

There are four positive integers not greater than 4: 1, 2, 3, and 4. Among them, we have two odd numbers: 1 and 3. Thus, the answer is \frac{2}{4} = 0.5.

Sample Input 2

5

Sample Output 2

0.6000000000

Sample Input 3

1

Sample Output 3

1.0000000000

Solution in PHP7 (7.0.15) (judge verdict: Accepted)

<?php
    // get input from stdin
    // $input = readline("Please input the number N: ");
    $input = readline();
    // Validate the input. 
    if(!is_numeric($input) || (int)$input < 1 || 100 < (int)$input) {
        throw new \Exception("Invalid input, please input between 1 and 100.", 1);
    }
    $input = (int)$input;
    
    // when value is odd <= please write. @dungnq-0076 
    if (($input % 2) != 0) {
        $prob = round((ceil($input / 2) / $input), 9); // <= this answer not 4, > 6 10^(-6)
        print_r($prob);
    }

    // // when value is even
    if(($input % 2) == 0) {
        echo(floatval(0.5));
    }
?>