#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 postorder(node*root)
{
    if(root != NULL){
    postorder(root->left);
    postorder(root->right);
    printf("%d",root->data);
    }
}
int main()
{
    int size,num;
    scanf("%d",&size);
    if(size<=0){
        printf("Invalid input");
        return 0;
    }
    for(i=0;i<size;i++)
    {
        scanf("%d",&n);
        root=insert(root,num);
        if(n<=0){
            printf("Invalid input")
            return 0;
        }
    }
    postorder(root);
    return 0;
}