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);
    
    }
} import java.util.*; util.* java 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);
    
    }
} 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);
    
    } main {
		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);
    
    } 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 int sum = 0; sum 0 while(true) {
          cnt++;
          
          sum += d + 1 + d;
          
          if(sum >= n) {
            break;
          }
        } true {
          cnt++;
          
          sum += d + 1 + d;
          
          if(sum >= n) {
            break;
          }
        } cnt++ cnt sum += d + 1 + d sum d + 1 + d d + 1 + d d 1 d if(sum >= n) {
            break;
          } sum >= n sum n {
            break;
          } break; System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args 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);
    
    }
} 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);
    
    }
} Main
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);
    
    }
}