#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);
       if(num>root->data);
       root->right=insert(root->left,num);
     retrun node;
}
void postorder{
    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);
         if(num<0)
         {
             printf("Invalid input");
         }
     }
     postorder(root);
     return 0;
 }