Problem:
Score : 100 points

Problem Statement

Find the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive). The order does not matter.

Constraints

2\leq K\leq 100

K is an integer.

Input

Input is given from Standard Input in the following format:

K

Output

Print the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive).

Sample Input 1

3

Sample Output 1

2

Two pairs can be chosen: (2,1) and (2,3).

Sample Input 2

6

Sample Output 2

9

Sample Input 3

11

Sample Output 3

30

Sample Input 4

50

Sample Output 4

625

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io::{self};

fn main() {
    let k: i32 = read_line().parse().unwrap();
    println!("{}", format!("{}", solve(k)));
}

fn solve(n: i32) -> i32 {
    let e = get_even_count(n);
    return e * (n - e);
}

fn get_even_count(n: i32) -> i32 {
    n / 2
}

fn read_line() -> String {
    let mut s = String::new();
    io::stdin().read_line(&mut s).unwrap();
    return s.trim_right().to_owned();
}