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

Node* create(int num)
{
    Node *newnode=(Node)malloc(sizeof(Node));
    newnode->data=num;
    newnode->left=NULL;
    newnode->right=NULL;
    return newnode;
}
Node *insert(Node *root,int num)
{
    if(root==NULL)
       return create(num);
    if(num<root->data)
       root->left=insert(root->left,num);
    if(num>root->data)
       root->right=insert(root->right,num);   
    return root;
}
void inorder(Node *root)
{
    if(root!=NULL)
    {
        inorder(root->left);
        printf("%d",root->data);
        inorder(root->right);
    }
}

int main()
{
    int size,itr;
    char num;
    scanf("%d",&size);
    if(size<0)
    {
        printf("Invalid input");
        return 0;
    }
    getch();
    for(itr=1;itr<=size*2;itr++)
    {
        scanf("%c",&num);
        if(num=='')
        continue;
        root=insert(root,num);
    }
    inorder(root);
    return 0;
    }
    
}