use std::io;

fn main() {
    let mut buf = String::new();
    io::stdin().read_line(&mut buf)
        .expect("Failed to read line");
    let n: i64 = buf.trim().parse()
        .expect("not integer");
    let l = (n-1) / 2 + 1;
    let ans = (l + 1) * l / 2;
    println!("{}", ans);
}