#include <stdio.h>
typedef struct TreeNode{
    int data;
}Node;
int main(){
    int N,L;
    if(!scanf("%d,%d",&L,&N!=2 ||N<=0||L<0||L>=N){
        printf("Invalid input");
        return 0;
    }
    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 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);
}