fn read<T: std::str::FromStr>() -> T
where
    <T as std::str::FromStr>::Err: std::fmt::Debug,
{
    let mut b = String::new();
    std::io::stdin().read_line(&mut b).unwrap();
    b.trim().parse().unwrap()
}

fn main() {
    let mut b = String::new();
    std::io::stdin().read_line(&mut b).unwrap();
    let iv: Vec<i32> = b
        .split(' ')
        .map(|x| x.trim().parse::<i32>().unwrap())
        .collect();
    let n = iv[0];
    println!("{}", n * (n + 1) / 2)
}