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: Runtime Error)

fn main() {
    // input
    let one = read_vec::<u64>();
    // A
    let a = one[0];
    // B
    let b = one[1];

    let a_uniq = get_uniq_koyakusus(a);
    let b_uniq = get_uniq_koyakusus(b);

    let mut ans = 1 as u64;

    for a in a_uniq {
        if b_uniq.contains(&a) {
            ans += 1;
        }
    }

    println!("{}", ans);
}

fn get_uniq_koyakusus(i: u64) -> Vec<u64> {
    let mut now = i;
    let mut ans = Vec::new();
    let mut koyakusu = 1;

    loop {
        koyakusu = get_min_koyakusu(now, koyakusu);
        if koyakusu == 0 {
            break;
        } else {
            ans.push(koyakusu);
            while now % koyakusu == 0 {
                now = now / koyakusu;
            }
        }
    }

    return ans;
}

fn get_min_koyakusu(i: u64, now: u64) -> u64 {
    for n in now + 1..(i + 1 / 2) + 1 {
        if i % n == 0 {
            return n;
        }
    }
    return 0;
}

#[allow(dead_code)]
fn read_line<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}
#[allow(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read_line::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}