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 Rust (1.15.1) (judge verdict: Accepted)

use std::io::BufRead;
use std::str::FromStr;

fn main() {
    let stdin = std::io::stdin();
    let mut t = Tokenizer::new(stdin.lock().lines().map(|x| x.unwrap()));

    let n: i32 = t.take();
    println!( "{}", problem( n ));
}

fn problem( n:i32 ) -> f64 {
    if n == 1 {
        return 1.0 as f64;
    }
    if n % 2 == 1 {
        return ((n/2+1) as f64)/(n as f64);
    }
    return 0.5 as f64;
}


#[cfg(test)]
mod test {
    use super::*;
    #[test]
    fn test1() {
        let result = problem( 5 );
        assert_eq!(result,vec![3,6,1]);
    }
}


struct Tokenizer<S: Iterator<Item = String>> {
    input: S,
    items: Vec<String>,
}

impl<S: Iterator<Item = String>> Tokenizer<S> {
    pub fn new(input: S) -> Self {
        Tokenizer {
            input: input,
            items: Vec::new(),
        }
    }

    pub fn take<T: FromStr>(&mut self) -> T {
        loop {
            if let Some(r) = self.items.pop() {
                return r.parse().ok().expect("parse failed");
            }
            let mut items = self
                .input
                .next()
                .unwrap()
                .split_whitespace()
                .map(|x| x.to_string())
                .collect::<Vec<String>>();
            items.reverse();
            self.items = items;
        }
    }
}