
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Integer n = scanner.nextInt();
        Integer d = scanner.nextInt();
        
        int result = 1;
        while(true) {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        }
    }
    
}

/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