import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;

        if (n % ((d * 2) + 1) == 0) {
            ans = n / ((d * 2) + 1);
        } else {
            ans = n / ((d * 2) + 1) + 1;
        }
        

        System.out.println(ans);

        sc.close();
    }    
}

/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