use std::io::*;
use std::str::*;

const MOD: i32 = 1000000007;

fn read<T: FromStr>() -> Option<T> {
    let stdin = stdin();
    let s = stdin
        .bytes()
        .map(|c| c.unwrap() as char)
        .take_while(|c| !c.is_whitespace())
        .collect::<String>();
    s.parse::<T>().ok()
}

fn main() {
    let n: usize = read().unwrap();
    let mut v = Vec::new();
    for i in 0..n {
        let tmp: i64 = read().unwrap();
        v.push(tmp);
    }
    v.sort();
    let diff = v[1] - v[0];
    if diff == 0 {
        println!("NO");
        return;
    }
    for i in 1..n {
        if v[i] - v[i - 1] != diff {
            println!("NO");
            return;
        }
    }
    println!("YES");
}