use std::io::*;

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: i64 = itr.next().unwrap().parse().unwrap();

    println!("{}", n / 2 + n / 2 * (n / 2 - 1));
}