import java.util.Scanner;
public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
   int N = sc.nextInt();
   int D = sc.nextInt();
  
   if(N <= (2*D + 1)){
     System.out.println(1);
   }else{
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   }
   
 }
} import java.util.Scanner; Scanner java.util public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
   int N = sc.nextInt();
   int D = sc.nextInt();
  
   if(N <= (2*D + 1)){
     System.out.println(1);
   }else{
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   }
   
 }
} Main public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
   int N = sc.nextInt();
   int D = sc.nextInt();
  
   if(N <= (2*D + 1)){
     System.out.println(1);
   }else{
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   }
   
 } main {
   Scanner sc = new Scanner(System.in);
   int N = sc.nextInt();
   int D = sc.nextInt();
  
   if(N <= (2*D + 1)){
     System.out.println(1);
   }else{
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   }
   
 } 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 if(N <= (2*D + 1)){
     System.out.println(1);
   }else{
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   } N <= (2*D + 1) N (2*D + 1) 2*D 2 D 1 {
     System.out.println(1);
   } System.out.println(1) System.out.println System.out System System.out 1 {
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   } int num = 0; num 0 while(N>0){
     N -= (2*D + 1);
      num++;
    } N>0 N 0 {
     N -= (2*D + 1);
      num++;
    } N -= (2*D + 1) N (2*D + 1) 2*D 2 D 1 num++ num System.out.println(num) System.out.println System.out System System.out num String[] args args public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
   int N = sc.nextInt();
   int D = sc.nextInt();
  
   if(N <= (2*D + 1)){
     System.out.println(1);
   }else{
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   }
   
 }
} public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
   int N = sc.nextInt();
   int D = sc.nextInt();
  
   if(N <= (2*D + 1)){
     System.out.println(1);
   }else{
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   }
   
 }
} Main
import java.util.Scanner;
public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
   int N = sc.nextInt();
   int D = sc.nextInt();
  
   if(N <= (2*D + 1)){
     System.out.println(1);
   }else{
     int num = 0;
    while(N>0){
     N -= (2*D + 1);
      num++;
    }
    System.out.println(num);
   }
   
 }
}