#include <stdio.h>
#include <stdlib.h>

typedef struct{
  int x;
  int y;
}Item;

typedef struct list{
  Item item;
  struct list *next;
}List;

List *list = NULL;

void push(int x,int y){
  List *new_node;
 
  new_node = (List*)malloc(sizeof(List));
  new_node->item.x = x;
  new_node->item.y = y;

  new_node->next = list;
  list = new_node;
}

Item pop(){
  Item item;
  List *next;

  if(list==NULL){
    printf("error\n");
    item.x=-1;
    return item;
  } else { 
    item = list->item;
    next = list->next;
    free(list);
    list = next;
    return item;
  }
}

int main(){
  Item item; 
  int i; 

  push(1,2);
  push(6,3);
  push(12,43);
  for(i=0;i<4;i++){
    item = pop();
    if(item.x>0){
      printf("%d %d\n",item.x,item.y);
    }
  }
}