#include<stdio.h>
#include<stdlib.h>
typedef struct node
{
    char data;
    struct node *left, *right;
}Node;
Node *root=NULL;
Node* create(char num)
{
    Node *newNode=(Node*) malloc (1 * sizeof(Node));
    newNode->data=num;
    newNode->left=NULL;
    newNode->right=NULL;
    return newNode;
}
Node* insert(Node *root,char num)
{
    if(root==NULL)
        return create(num);
    if(num<root->data)
        root->left=insert(root->left,num);
    else if(num>root->data)
        root->right=insert(root->right,num);
    return root;
}
void preorder(Node *root)
{
    if(root!=NULL)
    {
        printf("%c ",root->data);
        preorder(root->left);
        preorder(root->right);
    }
}
void inorder(Node *root)
{
    if(root!=NULL)
    {
        inorder(root->left);
        printf("%c ",root->data);
        inorder(root->right);
    }
}
void postorder(Node *root)
{
    if(root!=NULL){
        postorder("%c ",root->data);
        postorder(root->left);
        postorder(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;
}