import java.util.Scanner;
import java.util.InputMismatchException;

class Main {
   public static void main(String args[]) {
      int x=0 ,y=0;
      Scanner scanner = new Scanner(System.in);
      x = scanner.nextInt();
      y = scanner.nextInt();
      scanner.close();
      int kansi = y*2+1;
      if (x%kansi == 0) {
         System.out.println(x/kansi);
      } else {
         System.out.println(x/kansi + 1);
      }
   }
} import java.util.Scanner; Scanner java.util import java.util.InputMismatchException; InputMismatchException java.util class Main {
   public static void main(String args[]) {
      int x=0 ,y=0;
      Scanner scanner = new Scanner(System.in);
      x = scanner.nextInt();
      y = scanner.nextInt();
      scanner.close();
      int kansi = y*2+1;
      if (x%kansi == 0) {
         System.out.println(x/kansi);
      } else {
         System.out.println(x/kansi + 1);
      }
   }
} Main public static void main(String args[]) {
      int x=0 ,y=0;
      Scanner scanner = new Scanner(System.in);
      x = scanner.nextInt();
      y = scanner.nextInt();
      scanner.close();
      int kansi = y*2+1;
      if (x%kansi == 0) {
         System.out.println(x/kansi);
      } else {
         System.out.println(x/kansi + 1);
      }
   } main {
      int x=0 ,y=0;
      Scanner scanner = new Scanner(System.in);
      x = scanner.nextInt();
      y = scanner.nextInt();
      scanner.close();
      int kansi = y*2+1;
      if (x%kansi == 0) {
         System.out.println(x/kansi);
      } else {
         System.out.println(x/kansi + 1);
      }
   } int x=0 x 0 y=0; y 0 Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) x = scanner.nextInt() x scanner.nextInt() scanner.nextInt scanner y = scanner.nextInt() y scanner.nextInt() scanner.nextInt scanner scanner.close() scanner.close scanner int kansi = y*2+1; kansi y*2+1 y*2 y 2 1 if (x%kansi == 0) {
         System.out.println(x/kansi);
      } else {
         System.out.println(x/kansi + 1);
      } x%kansi == 0 x%kansi x kansi 0 {
         System.out.println(x/kansi);
      } System.out.println(x/kansi) System.out.println System.out System System.out x/kansi x kansi {
         System.out.println(x/kansi + 1);
      } System.out.println(x/kansi + 1) System.out.println System.out System System.out x/kansi + 1 x/kansi x kansi 1 String args[] args
import java.util.Scanner;
import java.util.InputMismatchException;

class Main {
   public static void main(String args[]) {
      int x=0 ,y=0;
      Scanner scanner = new Scanner(System.in);
      x = scanner.nextInt();
      y = scanner.nextInt();
      scanner.close();
      int kansi = y*2+1;
      if (x%kansi == 0) {
         System.out.println(x/kansi);
      } else {
         System.out.println(x/kansi + 1);
      }
   }
}
