fn main() {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).unwrap();
    let n = buf.trim().parse::<i32>().unwrap();
    // 標準入力難しいです...
    let mut ans = 0;
    for i in 1..n + 1 {
        ans += i;
    }
    println!("{}", ans);
}