#include<stdio.h>
#include<stdlib.h>
struct node{
    int data;
    struct Node*prev;
    struct node*next;
};
   struct node*createNode(int data){
       struct node*newnode=(structnode*)malloc(sizeof(struct node));
       newnode->data=data;
       newnode->prev=NULL;
       newnode->next=NULL;
       return newnode;
   }
   void append(struct node**head,struct node**tail,int data){
       struct node*newnode=createnode(data);
       if(*head==NULL){
           *head=*tail=newnode;
       }else{
           *head=*tail=newnode;
           newnode->prev=*tail;
           *tail=newnode;
       }
   }
   void display(struct node*head){
       struct node*temp=head;
       while(temp!=NULL){
           printf("%d",temp->data);
           if(temp-.next!=NULL){
               printf("");
           }
           temp=temp->next;
       }
       printf("\n");
   }
   int main(){
       int n,value;
       if(scanf("%d",&n)!1 ||n<=0){
           printf("invalid input\n");
           return 0;
            }
            struct node*head=NULL;
            struct node*tail=NULL;
            for (int i=0;i<n;i++){
                printf("invalid input\n");
                return 0;
         }
         append(&head,&tail,value);
   }
   display(head);
   return 0;
   }