import java.util.Scanner;
 
public class Main {
    static Scanner stdIn = new Scanner(System.in);
    public static void main(String[] args){
        int n = stdIn.nextInt();
        int d = stdIn.nextInt();

        System.out.println((int)Math.ceil((double)n / (2 * d + 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