#include<stdio.h>
#include<stdlib.h>
typedef struct node{
    int data;
    struct node*next;
    struct node*prev;
}node;

node*head=NULL,*tail;

void create(int num){
    node*newnode=(node**)malloc(1*sizeof(node));
    newnode->data=num;
    newnode->next=NULL;
    newnode->prev=NULL;
    if(head==NULL){
        head=newnode;
        tail=newnode;
    }
     else{
         tail->next=newnode;
         newnode->prev=tail;
         tail=newnode;
     }
}
void display(){
    Node*i;
    for(itr=head;i!=NULL;i=i->next){
        printf("%d",i->data);
    }
}
int main(){
    int n,num;
    scanf("%d",&n);
    if(n<=0){
        printf("Invalid input");
        return 0;
    }
    create(num);
}
display();
return 0;
}