#include<stdio.h>
typedef struct TreeNode{
    int data;
}Node;
int main(){
    int n,l;
    scanf("%d",&n);
    scanf("%d",&l);
    Node arr[n];
    for(int i=0;i<n;i++){
        scanf("%d",&arr[i].data);
    }
    int sum=0;
    int node=1;
    int level=0;
    int count=0;
    
    
    for(int i=0;i<n;i++){
        if(level==l)
            sum+=arr[i].data;
        count++;
        if(count==Node){
            level++;
            node*=2;
            count=0;
        }
    }
    printf("%d",sum);
}