fn main() {
    let mut nk = String::new();
    std::io::stdin().read_line(&mut nk).ok();
    let nk: Vec<usize> = nk.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nk[0] as isize;
    let k = nk[1] as isize;

    let minval = k * (n + n - k + 1) / 2;
    println!("{}", minval + 1);
}