import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main{
  public static void main(String[] args) throws IOException{
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    
    String[] line = br.readLine().split(" ");
    int n = Integer.parseInt(line[0]);
    int d = Integer.parseInt(line[1]);
    System.out.println(n/(2*d+1) + (n%(2*d+1) == 0 ? 0 : 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