#include<stdio.h>
#include<stdlib.h>
typedef struct node{
    int data;
    struct node *left,*right;
}Node;
Node *root=NULL;
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);
    else if(num>root->data)
    root->right=insert(root->right,num);
    return root;
}
void inOrder(Node *root){
    inOrder(root->left);
    printf("%c ",root->data);
    inOrder(root->right);
}
int main(){
    int n,num,itr;
    scanf("%d",&n);
    if(n<0){
        printf("Invalid input");
        return 0;
    }
    getchar();
    for(itr=1;itr<n*2;itr++){
        scanf("%c",&num);
        root=insert(root,num);
    }
    inOrder(root);
    return 0;
}