#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++){
       if(scanf("%d", &arr[i].data));
       printf("Invalid input");
       return 0;
    }
}
    int sum = 0;
    int count = 0;
    int node = 0;
    int level = 1;
    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);
}