use std::io;
use std::io::{Read, Stdin, stdin};

struct Input {
    n: i32,
}

fn main() {
    let mut stdin = io::stdin();
    let input = read_input(&mut stdin);
    solve(input);
}

fn read_input(stdin: &mut Stdin) -> Input {
    let mut s = String::new();
    stdin.read_line(&mut s).expect("can't read input.");

    let n = s.trim_end().parse::<i32>().expect("can't convert to integer");
    Input { n }
}

fn solve(input: Input) {
    let mut sum = 0;
    for i in 1..=input.n {
        sum += i;
    }
    println!("{}", sum);
}