use std::io::*;
use std::str::FromStr;

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parrse token")
}

fn main() {
    let n: i32 = read();
    let mut sum = 0;
    for i in 1..(n+1) {
        sum += i;
    }
    println!("{}", sum);
}