n = int(input())
a = list(map(int,input().split()))
if len(set(a)) != n:
    print('NO')
    exit(0)
a = sorted(a)
p = a[1] - a[0]
for i in range(n - 1):
    if p != a[i + 1] - a[i]:
        print('NO')
        exit(0)
print('YES')