#include<stdio.h>
#include<stdlib.h>
typedef struct node{
    char 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,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)
    {
        inOrder(root->left);
        printf("%d",root->data);
        
    }
}
int main(){
    int size,itr;
    char num;
    scanf("%d",&size);
    if(size<0){
        printf("Invalid input");
        return 0;
    }
    getchar();
    for(itr=0;itr<=size;itr++) {
        scanf("%c",&num);
        if(num == ' ')
        continue;
        root=insert(root,num);
        
    }
    inOrder(root);
    return 0;
}