#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+=curr[i].data;
    }
    count++;
    if(count==node){
        level++;
        count==0;
        node*=2;
        
    }
}
printf("%d",sum);
}