import java.util.Scanner;
public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
   int N = sc.nextInt();
   int D = sc.nextInt();
  
   if(N <= (2*D + 1)){
     System.out.println(1);
   }else{
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   }
   
 }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz