fn main() {
    let n: usize = get_a_value();
    let mut xv: Vec<u64> = get_line();

    xv.sort();
    xv.dedup();

    if xv.len() != n {
        println!("NO");
        return;
    }

    let delta = xv[1] - xv[0];
    for i in 2..n {
        if xv[i] - xv[i - 1] != delta {
            println!("NO");
            return;
        }
    }
    println!("YES");
}

#[allow(unused)]
fn get_a_value<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

#[allow(unused)]
fn get_line<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}