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

fn main() {
    let s = getline();
    let a: Vec<_> = s.trim().split(' ').collect();
    let x: i32 = a[0].parse().unwrap();
    let mut sum = 0;
    for i in 1..=x {
        sum += i;
    }
    println!("{}", sum);
}