fn get_input() -> String {
  let mut buffer = String::new();
  std::io::stdin().read_line(&mut buffer).expect("Failed");
  buffer
}

fn main() {
  let n = get_input().trim().parse::<i64>().unwrap();
  let v = (n - 1) / 2 + 1;

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