#include<stdio.h>
#include<stdlib.h>
typedef struct node{
    int data;
    struct node *right,*left;
} Node;

Node*root=NULL;
Node*create(char num){
    Node*newNode=(Node*)malloc(sizeof(Node));
    newNode->data=num;
    newNode->left=NULL;
    newNode->right=NULL;
    
}
Node *insert(Node *root,int num)
{
    if(root==NULL){
      return create(num);
      return root;
    }
    if(num<root->data){
       root->left=insert(root->left,num);
    }
     else if(num>root->data){
       root->right=insert(root->right,num);
     }
       return root;
}


void *inOrder(Node*root){
    if(root!=NULL){
        inOrder(root->left);
        printf("%c ",root->data);
        inOrder(root->right);
    }
}
int main(){
    int size,itr;
    char num;
    scanf("%d",&size);
    if(size<0){
        printf("Invalid input");
        return 0;
    }
    getchar();
    for(itr=1;itr<size*2;itr++){
        scanf(" %c",&num);
        if(num =='  '){
            continue;
        }
        root=insert(root,num);
    }
    inOrder(root);
    return 0;
}