N, xs = input(), [int(i) for i in input().split(' ')]
xs.sort()  # 昇順に並べる
distances = set()  # 距離
for i, x in enumerate(xs):
    if i != len(xs) - 1:
        distances.add(xs[i + 1] - x)
print('YES' if len(distances) == 1 and 0 not in distances else 'NO')