use std::io::{self, BufRead, BufReader, BufWriter, Write};

fn main() {
    let stdin = io::stdin();
    let mut stdin = BufReader::new(stdin.lock());
    let stdout = io::stdout();
    let mut stdout = BufWriter::new(stdout.lock());

    let n: u32 = read_line(&mut stdin).trim().parse().unwrap();

    let sum: u32 = (1..n + 1).sum();
    writeln!(&mut stdout, "{}", sum).unwrap();
}

fn read_line<R: BufRead>(reader: &mut R) -> String {
    let mut buf = String::new();
    reader.read_line(&mut buf).unwrap();
    buf
}