typedef struct unit {
    int data[20];
    struct unit *next;
} unit;

unit *copy(unit *start) {
    unit *newstart, *newrunning;
    for (newstart = newrunning = NULL; start != NULL; start = start->next) {
        unit *p = (unit*)malloc(sizeof(unit));
        *p = *start;
        p->next = NULL;
        if (newstart==NULL)
            newstart = newrunning = p;
        else {
            newrunning->next = p;
            newrunning = newrunning->next;
        }
    }
    return newrunning;
}