fn main() {
    let n: u32 = read();
    let s: u32 = (1..(n+1)).sum();
    println!("{}", s);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}