#include<stdio.h>
#include<stdlib.h>
typedef struct node{
    char data[];
    struct node *prev;
    struct node *next;
}Node;
Node *head=NULL,*tail;
void create(char *ch){
    Node *newnode=(Node*)malloc(sizeof(Node));
    strcpy(newnode->data,ch);
    newnode->prev=NULL;
    newnode->next=NULL;
    if(head==NULL){
        head=newnode;
        tail=newnode;
    }
    else{
        newnode->prev=tail;
        tail->next=newnode;
        tail=newnode;
    }
}
void display(){
    Node *itr=head;
    for(;itr!=head;itr=itr->prev){
        printf("%s ",itr->data);
    }
    printf("%s ",itr->data);
}
int main(){
    
}
int n;
scanf("%d",&n);
if(n<0){
    printf("Invalid input");
    return 0;
}
char ch[20];