import java.util.Scanner;
import java.lang.StringBuilder;
import java.math.BigInteger;

public class Main{
  
  
  
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    double n, d;
    n = sc.nextDouble();
    d = sc.nextDouble();
    
    System.out.println((int)Math.ceil(n/(2*d+1)));
    
    
    
    
    
    
//    System.out.println(time);
    
    
  }
}
/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