package main

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

func main() {
	sc.Split(bufio.ScanWords)
	N := nextInt()
	x := make([]int, N)
	for i := 0; i < N; i++ {
		x[i] = nextInt()
	}
	sort.Ints(x)
	z := x[1] - x[0]
	flag := true
	for i := 1; i < N; i++ {
		if x[i]-x[i-1] != z || z == 0 {
			flag = false
		}
	}
	if flag {
		fmt.Println("YES")
	} else {
		fmt.Println("NO")
	}
}


var sc = bufio.NewScanner(os.Stdin)

func nextLine() string {
    sc.Scan()
    return sc.Text()
}

func nextInt() int {
    i, _ := strconv.Atoi(nextLine())
    return i
}