import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
		int d = sc.nextInt();

        int cnt = 0;
        int sum = 0;
        while(true) {
          cnt++;
          
          sum += d + 1 + d;
          
          if(sum >= n) {
            break;
          }
        }
      
      
      	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