fn read_stdin() -> usize {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).unwrap();
    buf.trim().parse().unwrap()
}

fn solve(n: usize) -> usize {
    n * (n + 1) / 2
}

fn main() {
    let n = read_stdin();
    println!("{}", solve(n));
}