//ｺｯwwｺｯwwｺｹｯwwwｺｯwwｺｹｯwwwｺｹｯｺｯwwwｺｯwwｺｯwwｺｹｯwwwｺｯwwｺｹｯwwwｺｹｯｺｯwwwｺｹｰｰｰｰｯ!!!wwwwwｺｯwwｺｯwwｺｹｯwwwｺｯwwｺｹｯwwwｺｹｯｺｯwwwｺｯwwｺｯwwｺｹｯwwwｺｯwwwｺｹｯwwwｺｹｯｺｯwwwｺｹｰｰｰｰｯ!!!wwwwwｺｹｯｺｯｯｺｰｰｰｰ!!!!!!wwwwwwwwwww
import java.util.*;
public class Main {
    public static void main(final String[] args) {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        sc.close();
        int yono = n / (d * 2 + 1);
        if(n % (2 * d + 1) != 0) yono++;
        System.out.println(yono);
    }
}
/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