use std::io::stdin;
fn get_line() -> String {
    let mut s = String::new();
    stdin().read_line(&mut s).ok();
    s.trim().to_string()
}

fn main() {
    stdin().read_line(&mut String::new()).ok();

    let mut xs: Vec<i64> = get_line().split(' ').map(|x| x.parse().unwrap()).collect();

    xs.sort();

    let d = xs[1] - xs[0];
    let mut f = d != 0;

    for i in 1..(xs.len() - 1) {
        f = f && d == xs[i + 1] - xs[i];

        if !f {
            break;
        }
    }

    println!("{}",
        if f {
            "YES"
        }
        else {
            "NO"
        }
    );
}