class Problem0406:
	def solve(this):
		n = int(input())
		
		c1 = True
		res = {}
		for i in map(int, input().split()):
			res[i] = res.get(i, 0) + 1
			if res[i] >= 2:
				c1 = False
		
		t = sorted(list(res.keys()))
		c2 = {}
		for i in range(len(t) - 1):
			k = abs(t[i+1] - t[i])
			c2[k] = c2.get(k, 0) + 1
		
		if c1 and len(c2) == 1:
			print("YES")
		else:
			print("NO")
			
if __name__ == "__main__":
	problem = Problem0406()
	problem.solve()