#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);
    if(num>root->data)
        root->right=insert(root->right,num);
    return root;
}
int sum(Node *root,int level){
    if(root==NULL)
    return 0;
    if(level==0)
    return root->data;
    return sum(root->left,level -1)+sum(root->right,level-1);
    
}
int height(Node *root){
    if(root==NULL)
    return -1;
    int l=height(root->left);
    int r=height(root->right);
    return(1>r?1:r)+1;
}

int main(){
    int n,i,num;
    scanf("%d",&n);
    if(n<=0){
        printf("Invalid input");
        return 0;
    }
    for(i=0;i<n;i++){
        scanf("%d",&num);
        root=insert(root,num);
    }
    if(L < 0)||L>height(root)){
        printf("Invalid input");
        return 0;
    }
    printf("%d",sum(root, L));
    return 0;
  
}