import java.util.Scanner;
 public class Main {
 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
       int N = scanner.nextInt();
       int D = scanner.nextInt();
      
      int a =N/(D*2+1);
      
      if(N>D && N%(D*2+1)!=0){
       System.out.println(a+1);
      }
      else if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      }
 }
} import java.util.Scanner; Scanner java.util public class Main {
 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
       int N = scanner.nextInt();
       int D = scanner.nextInt();
      
      int a =N/(D*2+1);
      
      if(N>D && N%(D*2+1)!=0){
       System.out.println(a+1);
      }
      else if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      }
 }
} Main public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
       int N = scanner.nextInt();
       int D = scanner.nextInt();
      
      int a =N/(D*2+1);
      
      if(N>D && N%(D*2+1)!=0){
       System.out.println(a+1);
      }
      else if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      }
 } main {
        Scanner scanner = new Scanner(System.in);
       int N = scanner.nextInt();
       int D = scanner.nextInt();
      
      int a =N/(D*2+1);
      
      if(N>D && N%(D*2+1)!=0){
       System.out.println(a+1);
      }
      else if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      }
 } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int N = scanner.nextInt(); N scanner.nextInt() scanner.nextInt scanner int D = scanner.nextInt(); D scanner.nextInt() scanner.nextInt scanner int a =N/(D*2+1); a N/(D*2+1) N (D*2+1) D*2 D 2 1 if(N>D && N%(D*2+1)!=0){
       System.out.println(a+1);
      }
      else if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      } N>D && N%(D*2+1)!=0 N>D N D N%(D*2+1)!=0 N%(D*2+1) N (D*2+1) D*2 D 2 1 0 {
       System.out.println(a+1);
      } System.out.println(a+1) System.out.println System.out System System.out a+1 a 1 if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      } N>D && N%(D*2+1)==0 N>D N D N%(D*2+1)==0 N%(D*2+1) N (D*2+1) D*2 D 2 1 0 {
      System.out.println(a);
    } System.out.println(a) System.out.println System.out System System.out a if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      } N<=D N D {
      System.out.println("1");
      } System.out.println("1") System.out.println System.out System System.out "1" if(a<=0){
       System.out.println("1");
      } a<=0 a 0 {
       System.out.println("1");
      } System.out.println("1") System.out.println System.out System System.out "1" String[] args args public class Main {
 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
       int N = scanner.nextInt();
       int D = scanner.nextInt();
      
      int a =N/(D*2+1);
      
      if(N>D && N%(D*2+1)!=0){
       System.out.println(a+1);
      }
      else if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      }
 }
} public class Main {
 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
       int N = scanner.nextInt();
       int D = scanner.nextInt();
      
      int a =N/(D*2+1);
      
      if(N>D && N%(D*2+1)!=0){
       System.out.println(a+1);
      }
      else if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      }
 }
} Main
import java.util.Scanner;
 public class Main {
 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
       int N = scanner.nextInt();
       int D = scanner.nextInt();
      
      int a =N/(D*2+1);
      
      if(N>D && N%(D*2+1)!=0){
       System.out.println(a+1);
      }
      else if(N>D && N%(D*2+1)==0){
      System.out.println(a);
    }
      else if(N<=D){
      System.out.println("1");
      }
      else if(a<=0){
       System.out.println("1");
      }
 }
}