fn main() { let mut nk = String::new(); std::io::stdin().read_line(&mut nk).ok(); let nk: Vec = nk.trim().split_whitespace().map(|s| s.parse().unwrap()).collect(); let n = nk[0]; let k = nk[1]; let summary = k * (n+n-k+1) / 2; println!("{}", summary+1); }