use std::io::*;
use std::str::FromStr;
//use std::num;
//use std::cmp;
//use std::collections::VecDeque;
//use std::io::{self, BufRead};

fn main() {
	let n: usize = read();
	let mut x: Vec<isize> = vec![0; n];
	let mut abs = vec![0; n-1];
	let mut ans = 0;

	let len = x.len();

	for _i in 0..len{
		x[_i] = read();
	}

	for _i in 0..len{
		for _j in 0..len - _i - 1{
			if x[_j] < x[_j + 1]{
				x.swap(_j , _j + 1);
			}
		}
	}

	for _i in 1..len{
		abs[_i - 1] = (x[_i] - x[_i - 1]).abs();
	}

	for _i in 1..abs.len(){
		if abs[_i - 1] != abs[_i]{
			ans = 1;
		}
	}

	for _i in 1..x.len(){
		if x[_i - 1] == x[_i]{
			ans = 1;
		}
	}

	if ans == 0{
		print!("YES");
	}else{
		print!("NO");
	}
}

pub fn ctoi(c: char) -> isize {
	let n = c as isize - '0' as isize;

	return n;
}

pub fn stoi(c: String) -> isize {
	let n = c.parse::<isize>().unwrap();

	return n;
}

pub fn find_char(sentence: Vec<char>, target: char, start: isize) -> isize {
	for _i in start as usize..sentence.len() {
		if sentence[_i] == target {
			return _i as isize;
		}
	}
	return -1;
}

pub fn hex_to_binary(hex_string: &str, x: u32) -> Option<String> {
	match i64::from_str_radix(hex_string, x) {
		Ok(decimal) => Some(format!("{}", decimal)),
		Err(_) => None,
	}
}

pub fn my_floor(x: f64) -> f64 {
	let rounded = (x * 1000.0).floor() / 1000.0;

	rounded
}

pub fn upper_lower(x: char) -> char {
	let result: char;

	if x.is_uppercase() {
		result = x.to_ascii_lowercase();
	} else if x.is_lowercase() {
		result = x.to_ascii_uppercase();
	} else {
		result = x;
	}

	result
}

pub fn maxf_2(x: f64, y: f64) -> f64 {
	let result;

	if x >= y {
		result = x;
	} else {
		result = y;
	}

	result
}

pub fn max_2(x: isize, y: isize) -> isize {
	let result;

	if x >= y {
		result = x;
	} else {
		result = y;
	}

	result
}

pub fn max_u_2(x: usize, y: usize) -> usize {
	let result;

	if x >= y {
		result = x;
	} else {
		result = y;
	}

	result
}

pub fn min_2(x: isize, y: isize) -> isize {
	let result;

	if x >= y {
		result = y;
	} else {
		result = x;
	}

	result
}

pub fn min_2_i32(x: i32, y: i32) -> i32 {
	let result;

	if x >= y {
		result = y;
	} else {
		result = x;
	}

	result
}

pub fn max_3(x: isize, y: isize, z: isize) -> isize {
	let result;
	if x >= y && y >= z {
		result = x;
	} else if x >= z && z >= y {
		result = x;
	} else if y >= x && x >= z {
		result = y;
	} else if y >= z && z >= x {
		result = y;
	} else if z >= x && x >= y {
		result = z;
	} else {
		result = z;
	}

	result
}

pub fn max_u_3(x: usize, y: usize, z: usize) -> usize {
	let result;
	if x >= y && y >= z {
		result = x;
	} else if x >= z && z >= y {
		result = x;
	} else if y >= x && x >= z {
		result = y;
	} else if y >= z && z >= x {
		result = y;
	} else if z >= x && x >= y {
		result = z;
	} else {
		result = z;
	}

	result
}

pub fn min_3(x: usize, y: usize, z: usize) -> usize {
	let result;
	if x <= y && y <= z {
		result = x;
	} else if x <= z && z <= y {
		result = x;
	} else if y <= x && x <= z {
		result = y;
	} else if y <= z && z <= x {
		result = y;
	} else if z <= x && x <= y {
		result = z;
	} else {
		result = z;
	}

	result
}

pub fn min_u_3(x: usize, y: usize, z: usize) -> usize {
	let result;
	if x <= y && y <= z {
		result = x;
	} else if x <= z && z <= y {
		result = x;
	} else if y <= x && x <= z {
		result = y;
	} else if y <= z && z <= x {
		result = y;
	} else if z <= x && x <= y {
		result = z;
	} else {
		result = z;
	}

	result
}

pub fn read_text() -> String {
	let mut word = String::new();
	std::io::stdin().read_line(&mut word).ok();
	let answer = word.trim().to_string();

	answer
}

pub fn read_array() -> Vec<char> {
	let array: String = read();
	let chars: Vec<char> = array.trim().chars().collect::<Vec<char>>();
	chars
}

pub fn read<T: FromStr>() -> T {
	let stdin = stdin();
	let stdin = stdin.lock();
	let token: String = stdin
		.bytes()
		.map(|c| c.expect("failed to read char") as char)
		.skip_while(|c| c.is_whitespace())
		.take_while(|c| !c.is_whitespace())
		.collect();
	token.parse().ok().expect("failed to parse token")
}