import java.util.Scanner;
public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = 0;
    for(int i = 1;;i++){
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    }
  }
} import java.util.Scanner; Scanner java.util public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = 0;
    for(int i = 1;;i++){
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    }
  }
} Main public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = 0;
    for(int i = 1;;i++){
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    }
  } main {
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = 0;
    for(int i = 1;;i++){
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    }
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc int c = 0; c 0 for(int i = 1;;i++){
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    } int i = 1; int i = 1; i 1 i++ i++ i {
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    } {
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    } c += 2 * b + 1 c 2 * b + 1 2 * b 2 b 1 if(a <= c){
        System.out.println(i);
        break;
      } a <= c a c {
        System.out.println(i);
        break;
      } System.out.println(i) System.out.println System.out System System.out i break; String args[] args public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = 0;
    for(int i = 1;;i++){
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    }
  }
} public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = 0;
    for(int i = 1;;i++){
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    }
  }
} Main
import java.util.Scanner;
public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = 0;
    for(int i = 1;;i++){
      c += 2 * b + 1;
      if(a <= c){
        System.out.println(i);
        break;
      }
    }
  }
}