fn get_line() -> String {
    let mut ret = String::new();
    std::io::stdin().read_line(&mut ret).ok();
    ret
}

fn main() {
    let line = get_line();
    let n: usize = line.trim().parse().unwrap();
    let result: usize = (1..n + 1).into_iter().sum();
    println!("{}", result);
}