import 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();
    
    int m = D*2+1;
    int ans = N/m;

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

    if(N%m==0){
        System.out.println(ans);
    }else{
        System.out.println(ans+1);
 }
}
} Main public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int m = D*2+1;
    int ans = N/m;

    if(N%m==0){
        System.out.println(ans);
    }else{
        System.out.println(ans+1);
 }
} main {
    
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int m = D*2+1;
    int ans = N/m;

    if(N%m==0){
        System.out.println(ans);
    }else{
        System.out.println(ans+1);
 }
} 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 int m = D*2+1; m D*2+1 D*2 D 2 1 int ans = N/m; ans N/m N m if(N%m==0){
        System.out.println(ans);
    }else{
        System.out.println(ans+1);
 } N%m==0 N%m N m 0 {
        System.out.println(ans);
    } System.out.println(ans) System.out.println System.out System System.out ans {
        System.out.println(ans+1);
 } System.out.println(ans+1) System.out.println System.out System System.out ans+1 ans 1 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();
    
    int m = D*2+1;
    int ans = N/m;

    if(N%m==0){
        System.out.println(ans);
    }else{
        System.out.println(ans+1);
 }
}
} public class Main {
    public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int m = D*2+1;
    int ans = N/m;

    if(N%m==0){
        System.out.println(ans);
    }else{
        System.out.println(ans+1);
 }
}
} Main
import 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();
    
    int m = D*2+1;
    int ans = N/m;

    if(N%m==0){
        System.out.println(ans);
    }else{
        System.out.println(ans+1);
 }
}
}