fn get_line() -> String {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    return s;
}
fn main() {
    let s = get_line();
    let n: i32 = s.trim().parse().unwrap();
    let a = (1 + n) * n / 2;

    println!("{}", a);
}