use std::io;

fn main() {
    let mut str = String::new();
    io::stdin().read_line(&mut str).ok().expect("error");
    let n : u64 = str.trim().parse().ok().expect("error");
    let mut s : u64 = 0;
    for i in 1 .. n + 1 {
        s += i;
    }
    println!("{}", s);
}