#[allow(unused)]
use proconio::{input, marker::Chars};

fn main() {
    input! {
        d: usize,
    }
    if d < 4 {
        println!("0")
    } else {
        let mut ans = 0;
        for i in 1..=d / 2 {
            let j = (d - i * 2) / 2;
            ans = ans.max(i * j);
        }
        println!("{}", ans)
    }
}