use std::io;

fn main () {
    let mut num = String::new();

    io::stdin().read_line(&mut num)
        .expect("Faild to read line.");

    let num: u32 = num.trim().parse().unwrap();

    let sum: u32 = (1..num+1).fold(0, |sum, a| sum + a);

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