两个链表的排序问题，如何解决？

题：将a,b两个链表连接起来并按升序排列。

#include<stdio.h>
#include<malloc.h>
#define LEN sizeof(struct Student)
struct Student
{
    long num;
    int score;
    struct Student* next;
};
int main()
{
    struct Student* Creat_List(void);
    struct Student* Insert(struct Student* ahead, struct Student* bhead);
    void Print(struct Student* ahead);
    struct Student* ahead, * bhead, * abhead;
    printf("list a:\n");
    ahead = Creat_List();
    printf("list b:\n");
    bhead = Creat_List();
    abhead = Insert(ahead, bhead);
    Print(abhead);
    return 0;
}
struct Student* Creat_List(void)
{
    int n = 0;
    struct Student* p1, * p2, * head=NULL;
    p1 = p2 = (struct Student*)malloc(LEN);
    scanf_s("%ld %d", &p1->num, &p1->score);
    while (p1->num != 0)
    {
        n = n + 1;
        if (n == 1)
            head = p1;
        else
            p2->next = p1;
        p2 = p1;
        p1 = (struct Student*)malloc(LEN);
        scanf_s("%ld %d", &p1->num, &p1->score);
    }
    p2->next = NULL;
    return head;
}
struct Student* Insert(struct Student* ahead, struct Student* bhead)
{
    struct Student* pa1, * pa2, * pb1, * pb2;
    pa1 = pa2 = ahead;
    pb1 = pb2 = bhead;
    do
    {
        while ((pa1->num < pb1->num) && (pa1->next != NULL))
        {
            pa2 = pa1;
            pa1 = pa1->next;
        }
        if (pa1->num >= pb1->num)
        {
            if (pa1 == ahead)
                ahead = pb1;
            else
                pb2->next = pb1;
            pb1 = pb1->next;
            pb2->next = pa1;
            pa2 = pb2;
            pb2 = pb1;
        }
    } while ((pa1->next != NULL) || (pa1 == NULL && pb1 != NULL));
    if ((pb1 != NULL) && (pb1->num > pa1->num) && (pa1->next == NULL))
        pa1->next = pb1;
    return ahead;
}
void Print(struct Student* ahead)
{
    struct Student* p;
    p = ahead;
    while (p != NULL)
    {
        printf("%ld %d\n", p->num, p->score);
        p = p->next;
    }
}

结果为什么这样了？

另外：有无hxd梳理一下它这个Insert函数的思路，大脑有点混乱。尤其没明白那个do.while.循环条件。

将a,b两个链表连接起来，【并按升序排列】
不仅是插入，而是两个链表接元素的大小交替合并
并且：
a,b本身也是升序链表，否则Insert()也完成不任务的