def main():
    N = int(input())
    A = sorted(map(int, input().split()))
    for i in range(N-1):
        if A[i] - A[i+1] != A[0] - A[1]:
            print('NO')
            return
    if A[0] == A[1]:
        print('NO')
    else:
        print('YES')


if __name__ == '__main__':
    main()