def kamokan(n, x):
    q, r = divmod((x[-1] - x[0]),  (n - 1))
    if r == 1 or len(set(x)) != n:
        print("NO")
        return
    for i in range(1, n):
        if q != x[i] - x[i - 1]:
            print("NO")
            break
    else:
        print("YES")
    return

n = int(input())
x = sorted([int(i) for i in input().split()])

kamokan(n, x)