use std::io::stdin;

#[allow(dead_code)]
fn getline() -> String {
    let mut input = String::new();
    stdin().read_line(&mut input).ok();
    return input;
}

#[allow(dead_code)]
pub fn sum(num: i32) -> i32 {
    let mut result = 0;
    for num in 1..num + 1 {
        result += num;
    }
    return result;
}

#[allow(dead_code)]
fn main() {
    let s = getline();
    let num: i32 = s.trim().parse::<i32>().unwrap();
    println!("{}", sum(num));
}