import java.util.*;

class Main{
	public static void main(String[] args){
      Scanner sc = new Scanner(System.in);
      
	  int n = sc.nextInt();
      int d = sc.nextInt();
      int cnt = 0;
      
      while(n > 0){
      	n -= d*2 + 1;
        cnt++;
      }
      
      System.out.println(cnt);
    }
}
/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