

import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int trees = sc.nextInt();
        int inspector = sc.nextInt();
        int a = 2*inspector + 1;
        int ans = 0;
        if (trees % a == 0) {
            ans = trees /a;
        } else {
            ans = (trees/a) + 1;
        }
        
        System.out.print(ans);
    }
}
/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