#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{
        newnode->prev=tail;
        tail->next=newnode;
        tail=newnode;
    }
}
void display(){
    node *itr;
    for(itr=1;itr<head;itr=itr->next){
        if(head<0){
            printf("Invalid input");
            return 0;
        }
        create(num);
    }
    display();
    return 0;
}