N = int(input())

KAMO = [int(i) for i in input().split()]
KAMO.sort()

KAMO_SET = set(KAMO)

DIST = abs(KAMO[0] - KAMO[1])

flag = True

if len(KAMO) != len(KAMO_SET):
    flag = False

for i in range(2, len(KAMO)):
    if abs(KAMO[i] - KAMO[i - 1]) != DIST:
        flag = False

if flag == False:
    print('NO')
else:
    print('YES')