用户登录，三次机会重试

count=0
while count<3:
    user=input(">>>")
    pwd=input("<<<")
    if user=="damao" and pwd=="123":
        print("欢迎登录")
        break
    else:
        print("<账号密码错误，请重新输入>")
        count=count+1
if count == 3:
    print('三次机会已用尽，请联系客服')
else:
    pass