# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	N = int(input())
	X = getlist()
	X.sort()
	D = defaultdict(int)
	for i in range(N - 1):
		if X[i + 1] - X[i] == 0:
			print("NO")
			return
		D[X[i + 1] - X[i]] += 1

	if len(D) >= 2:
		print("NO")
	else:
		print("YES")



if __name__ == '__main__':
	main()