use std::io::{self, Read};

fn read_stdin<'a>() -> Vec<String> {
    let mut buffer = String::new();
    io::stdin().read_to_string(&mut buffer).ok();
    buffer.trim().split('\n').map(|s| s.to_string()).collect()
}

fn main() {
    let s = read_stdin().first().unwrap().parse::<i32>().unwrap();
    println!("{:?}", (0..s + 1).sum::<i32>());
}