struct node {
    int data;
    struct node *next;
    struct node *prev;
};

struct node *start = NULL; // pointer to start of list.
struct node *end = NULL; // pointer to end of list

struct node * create (data)
    int data;
{
    struct node *temp = (struct node *)malloc(sizeof(struct node));
    temp->data = data;
    temp->next = temp->prev = NULL;
    return temp;
}

struct node * push(start, temp)
    struct node *start;
    struct node *temp;
{
    if(start == NULL) {
        // this node is the first node, assign it as is.
        start = temp;
    } else {
        temp->next = start;
        start->prev = temp;
        start = temp;
    }
    return start;
}