def readint():
    return int(input())

def readints():
    return list(map(int, input().split()))

def calc(xs):
    ys = sorted(xs)
    s = set([a - b for a, b in zip(ys, ys[1:])])
    return len(s) == 1 and 0 not in s

def main():
    readint()
    xs = readints()
    print("YES" if calc(xs) else "NO")

if __name__ == "__main__":
    main()