// editor2
#include<stdio.h>
typedef struct TreeNode{
    int data;
}Node;
int main(){
    int size,l;
    scanf("%d",&size);
    scanf("%d",&l);
    int arr[size];
    for(int i=0;i<size;i++){
        scanf("%d",&arr[i].data);
    }
    int count=0;
    int node=1;
    int sum=0;
    int level=0;
    int reached=0;
    if(level==l){
        sum+=arr[i].data;
        reached=1;
    }
    count++;
    if(count==node){
        level++;
        node*=2;
        count=0;
    }
    printf("%d",sum);
    return 0;
}