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

typedef struct SNode_
{
  struct SNode_ *prev, *next;
  int v;
} SNode;

typedef struct SList2_
{
  SNode *first, *last, *cur;
} SList2;

void Add(SList2 *l, int v);
void Scan(SList2 *l, int n);
void Print(SList2 *l);
SList2 *Create(void);

SList2 *Create(void)
{
  SList2 *l;
  l = (SList2*)malloc(sizeof(*l));
  l -> cur = l -> first = l -> last = NULL;
  return l;
}



void Add(SList2 *l, int v)
{
  SNode *n;
  n = (SNode*)malloc(sizeof(*n));
  n -> v = v;
  n -> prev = n -> next = NULL;
  if (l -> cur == NULL)
  {
    l -> cur = l -> first = l -> last = n;
  }
  else
  {
    n -> prev = l -> cur;
    n -> next = l -> cur -> next;
    l -> cur -> next = n;
    if (n -> next) n -> next -> prev = n;
    else l -> last = n;
  }
}

void Scan(SList2 *l, int n)
{
  int x = n + 1;
  for (int i = 0; i < n; i++)
  {
    x -= 1;
    Add(l, x);
  }
}

void Print(SList2 *l)
{
  SNode *n = l -> first;
  printf("%d", n -> v);
  while (l -> cur != NULL)
  {
    printf("%d", n -> v);
    if (n -> next != NULL)
    {
      n = n -> next;
    }
  }
}

int main(void)
{
 SList2 *l;
 l = Create();
 Scan(l, 6);
 Print(l);
 return 0;
}