#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);
    elseif(num>root->data)
    root->right=insert(root->right,num)
}
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(int i=0;i<size;i++)
    {
    scanf("%d",&num);
    root=insert(root,num);
        if(num<=0)
        {
            printf("Invalid input");
            return 0;
        }
    postorder(root);
    return 0;
    }
}