use std::collections::HashSet;

fn main() {
    let mut xx = String::new();
    std::io::Read::read_to_string(&mut std::io::stdin(), &mut xx).ok();
    let mut xx: Vec<u64> = xx
        .split_whitespace()
        .skip(1)
        .map(|n| n.parse().unwrap())
        .collect();

    xx.sort_unstable();

    let distances: HashSet<u64> = xx.windows(2).map(|x| x[1] - x[0]).collect();

    if distances.len() == 1 && !distances.contains(&0) {
        println!("YES");
    } else {
        println!("NO");
    }
}