#include <stdio.h>
#include <stdlib.h>
struct Node {  // SINGLY LINKED LIST
    int    value;
    struct Node* prev;
    struct Node* next;
}; // require ≥20 bytes

int main(int argc, char *argv[]) {
    // empty list
    struct Node* head = NULL; // always set head to either NULL or malloc(…)
    struct Node* tail = NULL;
    
    head = malloc(sizeof(*head));  // allocated ≥20 bytes [OOP]
    tail = head;
    head -> value = 2;
    head -> prev  = NULL;

    // WE ARE HERE as of 11:07 AM
    head -> next          = malloc( sizeof(*(head -> next)) );
    head -> next -> value = 4;
    head -> next -> prev  = head;
    head -> next -> next  = NULL;
    tail                  = head -> next;
    // FILL IN TO HERE  

    free(head -> next);
    free(head);

    return EXIT_SUCCESS;
}
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