#include<stdio.h>

typedef struct TreeNode{
    int data;
}node;

int main(){
    int N,L;
    if(!scanf("%d",&N)||N<0){
        printf("Invalid input");
        return 0;
    }
    if(!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);
    return 0;
}