import java.util.Scanner;
 public class Main {
 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
       int N = scanner.nextInt();
       int D = scanner.nextInt();
      
      int a =N/(D*2+1);
      
      if(N>D && N%(D*2+1)!=0){
       System.out.println(a+1);
      }
      else if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      }
 }
}
/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