package main

import (
	"fmt"
	"sort"
)

func main() {
	var N int
	fmt.Scan(&N)
	x := make([]int, N)
	for i := 0; i < N; i++ {
		fmt.Scan(&x[i])
	}
	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")
	}
}