n = int(input())
x = list(map(int,input().split()))
x_so = sorted(x)
che = []
che_er = False

for i in range(1, n):
	che.append(x_so[i] - x_so[i - 1])
	if x_so[i] - x_so[i - 1] == 0:
	    che_er = True
	    break
che_set = set(che)

if che_er:
    print('NO')
elif (len(che_set) == 1):
    print('YES')
else:
    print('NO')