use std::io::*;

#[derive(Debug)]
struct Input {
    n: i32,
}

fn next_token(cin_lock: &mut StdinLock) -> String {
    cin_lock.by_ref().bytes().map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect::<String>()
}

fn read_input(cin_lock: &mut StdinLock) -> Input {
    Input {
        n: next_token(cin_lock).parse().expect("n"),
    }
}

fn solve(input: &Input) {
    let sum = input.n * (input.n + 1) / 2;
    println!("{}", sum);
}

fn main() {
    let cin = stdin();
    let mut cin_lock = cin.lock();

    let input = read_input(&mut cin_lock);
    solve(&input);
}