def game_21():
    print("游戏开始")
    print("甲报数：1")
    A =1
    def win():
        if(A==21):
            print("甲赢")
        if(B==21):
            print("乙赢")
    while True:
        while True:
            B = int(input('乙报数：'))
            # 保证第二个录入大于1小于3，到21就判断赢
            if B - A > 3 or B - A <= 0:
                print('不符合规则,重新输入\n')
            elif B == 21:
                return win()
            else:
                break
        while True:
            A=A+4
            print('