import java.util.*;

public class Main{
	public static void main(String args[]){
    	Scanner scanner = new Scanner(System.in);
        int tree = scanner.nextInt();
        int patrol_width = scanner.nextInt();
      
        int max_patrol = patrol_width * 2 + 1;
      
        for(int i = 1; i <= 20; i++){
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        }
    }
}
/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