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 Ruby (2.3.3) (judge verdict: Runtime Error)

a, b = gets.split("\s").map(&:to_i)
c = a < b ? a : b
c = Math.sqrt(c).floor
result= 1
table = Array.new(c + 1, true)

(2..c).each do |num|
  if table[num]
    if a % num == 0 && b % num == 0
      result += 1
    end
    k = num*num
    while k <= c
      table[k] = false
      k += num
    end
  end
end

puts result