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);
    }
} import java.util.*; util.* java 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);
    }
} 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);
    } main {
      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);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int d = sc.nextInt(); d sc.nextInt() sc.nextInt sc int cnt = 0; cnt 0 while(n > 0){
      	n -= d*2 + 1;
        cnt++;
      } n > 0 n 0 {
      	n -= d*2 + 1;
        cnt++;
      } n -= d*2 + 1 n d*2 + 1 d*2 d 2 1 cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args
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);
    }
}