use std::io;

fn main() {
    let mut num_s = String::new();
    io::stdin().read_line(&mut num_s).ok();
    let num: i32 = num_s.trim().parse().unwrap();

    let mut sum: i32 = 0;

    for n in 1..num + 1 {
        sum += n;
    }

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