import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
       
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int count = 1;
        int c = b + 1;
        while(a > (c + b)){
            count++;
            c = c + 2 * b + 1;
        }
        System.out.print(count);
	}
}
/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