from collections import Counter

n = int(input())
kamo = sorted([int(i) for i in input().split()], reverse=True)

isDuplicate = False
distance_list = []

counter = Counter(kamo)
if (set([len(Counter(kamo))]) - {1}) == set():
    isDuplicate = True


for i in range(len(kamo) - 1):
    distance = 0
    distance = kamo[i] - kamo[i + 1]
    distance_list.append(distance)


if not isDuplicate and (len(set(distance_list)) == 1):
    print("YES")
else:
    print("NO")