package main

import (
	"bufio"
	"os"
	"strings"
	"strconv"
	"sort"
	"fmt"
)

func main() {
	N := largeInt()
	x := largeIntArray()

	sort.Ints(x)

	diff := x[1] - x[0]
	if diff == 0 {
		fmt.Println("NO")
		return
	}
	for i := 1; i < N; i++ {
		if diff != x[i] - x[i - 1] {
			fmt.Println("NO")
			return
		}
	}
	fmt.Println("YES")
	return
}

var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func readLine() string {
	buf := make([]byte, 0, 1000000)
	for {
		l, p, e := rdr.ReadLine()
		if e != nil {
			panic(e)
		}
		buf = append(buf, l...)
		if !p {
			break
		}
	}
	return string(buf)
}
func largeInt() (ret int) {
	s := readLine()
	ret, e := strconv.Atoi(s)
	if e != nil {
		panic(e)
	}
	return
}

func largeIntArray() []int {
	s := readLine()
	vs := strings.Split(s, " ")
	N := len(vs)
	data := make([]int, N)
	for i := 0; i < N; i++ {
		var e error
		data[i], e = strconv.Atoi(vs[i])
		if (e != nil) {
			panic(e)
		}
	}
	return data
}