use proconio::{fastout, input};

#[fastout]
fn main() {
    input! {
        p: i32,
		q: i32,
		r: i32,
    }

    println!("{}", output(solve(p, q, r)));
}

fn solve(p: i32, q: i32, r: i32) -> bool {
    q * 2 == p + r
}

fn output(ans: bool) -> &'static str {
	match ans {
		true => "Yes",
		false => "No",
	}
}