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: Accepted)

def gi; gets.to_i end
def gs; gets.chomp end
def gli; gets.split(' ').map(&:to_i) end
def d(n); Math.log10(n).to_i + 1 end
class Integer
  # 約数の組み合わせを列挙する
  def divisor_combinations
    (1..Math.sqrt(self).to_i).
      select { |i| self % i == 0 }.
      map { |i| [i, self / i] }
  end
end

N = gi

all = (1..N).to_a
odds = all.select(&:odd?)
puts odds.length.to_f / all.length