import java.util.*;
public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    float n = sc.nextFloat();
    float d = sc.nextFloat();
    float nd = n/((2*d)+1);
    int nd2 = (int)n/((2*(int)d)+1);
    if(n%((2*d)+1)>0){
      System.out.println(nd2+1);
    }else{
      System.out.println(nd2);
    } 
  }
} import java.util.*; util.* java public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    float n = sc.nextFloat();
    float d = sc.nextFloat();
    float nd = n/((2*d)+1);
    int nd2 = (int)n/((2*(int)d)+1);
    if(n%((2*d)+1)>0){
      System.out.println(nd2+1);
    }else{
      System.out.println(nd2);
    } 
  }
} Main public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    float n = sc.nextFloat();
    float d = sc.nextFloat();
    float nd = n/((2*d)+1);
    int nd2 = (int)n/((2*(int)d)+1);
    if(n%((2*d)+1)>0){
      System.out.println(nd2+1);
    }else{
      System.out.println(nd2);
    } 
  } main {
    Scanner sc = new Scanner(System.in);
    float n = sc.nextFloat();
    float d = sc.nextFloat();
    float nd = n/((2*d)+1);
    int nd2 = (int)n/((2*(int)d)+1);
    if(n%((2*d)+1)>0){
      System.out.println(nd2+1);
    }else{
      System.out.println(nd2);
    } 
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) float n = sc.nextFloat(); n sc.nextFloat() sc.nextFloat sc float d = sc.nextFloat(); d sc.nextFloat() sc.nextFloat sc float nd = n/((2*d)+1); nd n/((2*d)+1) n ((2*d)+1) (2*d) 2 d 1 int nd2 = (int)n/((2*(int)d)+1); nd2 (int)n/((2*(int)d)+1) (int)n ((2*(int)d)+1) (2*(int)d) 2 (int)d 1 if(n%((2*d)+1)>0){
      System.out.println(nd2+1);
    }else{
      System.out.println(nd2);
    } n%((2*d)+1)>0 n%((2*d)+1) n ((2*d)+1) (2*d) 2 d 1 0 {
      System.out.println(nd2+1);
    } System.out.println(nd2+1) System.out.println System.out System System.out nd2+1 nd2 1 {
      System.out.println(nd2);
    } System.out.println(nd2) System.out.println System.out System System.out nd2 String args[] args public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    float n = sc.nextFloat();
    float d = sc.nextFloat();
    float nd = n/((2*d)+1);
    int nd2 = (int)n/((2*(int)d)+1);
    if(n%((2*d)+1)>0){
      System.out.println(nd2+1);
    }else{
      System.out.println(nd2);
    } 
  }
} public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    float n = sc.nextFloat();
    float d = sc.nextFloat();
    float nd = n/((2*d)+1);
    int nd2 = (int)n/((2*(int)d)+1);
    if(n%((2*d)+1)>0){
      System.out.println(nd2+1);
    }else{
      System.out.println(nd2);
    } 
  }
} Main
import java.util.*;
public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    float n = sc.nextFloat();
    float d = sc.nextFloat();
    float nd = n/((2*d)+1);
    int nd2 = (int)n/((2*(int)d)+1);
    if(n%((2*d)+1)>0){
      System.out.println(nd2+1);
    }else{
      System.out.println(nd2);
    } 
  }
}