fn cc_read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    return s.trim().parse().ok().unwrap();
}

fn main() {
    let n: i32 = cc_read();
    println!("{}", n * (n + 1) / 2);
}