#!/usr/bin/env pypy3
# btkさんの解 http://yukicoder.me/submissions/108104 を踏まえて

import sys


def main():
    n = int(input())
    # {x_i}を受け取ってソートする
    xs = sorted(map(int, input().split()))
    # 階差数列の最大値・最小値を求める
    d_min = sys.maxsize
    d_max = -sys.maxsize
    for i in range(n - 1):
        d = xs[i + 1] - xs[i]
        d_min = min(d_min, d)
        d_max = max(d_max, d)
    print("YES" if d_min == d_max != 0 else "NO")


if __name__ == '__main__':
    main()