本关任务：编写函数函数功能是：统计整数n的各位上出现数字1、2、3的次数。要求输入输出均在主函数中完成。

def count_digits(n):
    count_1 = 0
    count_2 = 0
    count_3 = 0
    
    while n > 0:
        digit = n % 10
        if digit == 1:
            count_1 += 1
        elif digit == 2:
            count_2 += 1
        elif digit == 3:
            count_3 += 1
        n //= 10
    
    return count_1, count_2, count_3

def main():
    n = int(input("请输入一个整数："))
    count_1, count_2, count_3 = count_digits(n)
    print("数字1出现的次数：", count_1)
    print("数字2出现的次数：", count_2)
    print("数字3出现的次数：", count_3)

main()