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

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

if (len(che_set) == 1) and che_set != 0:
    print('YES')
else:
    print('NO')