// editor1
#include<stdio.h>
#include<stdlib.h>
typedef struct node{
    int data;
    struct node *left;
    struct node *right;
}nd;
nd *create(int num){
    nd *newnode=(nd*)malloc(sizeof(nd));
    newnode->data=num;
    newnode->left=NULL:
    newnode->right=NULL;
    return newnode;
}
nd *build(int a[],n,i){
    if(i<=0 || a[i]==0)
     return NULL:
     nd *root=create(num);
     root->left=build(a,n,2*i+1);
     root->right=build(a,n,2*i+2);
     return root;
}
void in(nd *root){
    nd *s[100];
    int top=-1;
    nd *curr=root;
    while(curr!=NULL||top!=-1){
        while(curr!=NULL){
            s[++top]=curr;
            curr=curr->left;
        }
        curr=s[top--];
        printf("%d",curr->data);
        curr=curr->right;
    }
}
int main(){
    int n;
    scanf("%d",&n);
    if(n<=0){
        printf("Invalid input");
        return 0;
    }
    int a[n];
    for(int i=0;i<n;i++){
        scanf("%d",&a[i]);
    }
    nd *root=build(a,n,0);
    in(root);
    return 0;
}