import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner s = new Scanner(System.in);
        String[] z =s.nextLine().split(" ");
        int n=Integer.parseInt(z[0]);
        int d=Integer.parseInt(z[1])*2+1;
        for(int i=1;i<= 1000;i++){
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        }
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args){
        Scanner s = new Scanner(System.in);
        String[] z =s.nextLine().split(" ");
        int n=Integer.parseInt(z[0]);
        int d=Integer.parseInt(z[1])*2+1;
        for(int i=1;i<= 1000;i++){
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        }
    }
} Main public static void main(String[] args){
        Scanner s = new Scanner(System.in);
        String[] z =s.nextLine().split(" ");
        int n=Integer.parseInt(z[0]);
        int d=Integer.parseInt(z[1])*2+1;
        for(int i=1;i<= 1000;i++){
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        }
    } main {
        Scanner s = new Scanner(System.in);
        String[] z =s.nextLine().split(" ");
        int n=Integer.parseInt(z[0]);
        int d=Integer.parseInt(z[1])*2+1;
        for(int i=1;i<= 1000;i++){
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        }
    } Scanner s = new Scanner(System.in); s new Scanner(System.in) String[] z =s.nextLine().split(" "); z s.nextLine().split(" ") s.nextLine().split s.nextLine() s.nextLine s " " int n=Integer.parseInt(z[0]); n Integer.parseInt(z[0]) Integer.parseInt Integer z[0] z 0 int d=Integer.parseInt(z[1])*2+1; d Integer.parseInt(z[1])*2+1 Integer.parseInt(z[1])*2 Integer.parseInt(z[1]) Integer.parseInt Integer z[1] z 1 2 1 for(int i=1;i<= 1000;i++){
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        } int i=1; int i=1; i 1 i<= 1000 i 1000 i++ i++ i {
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        } {
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        } if(n <= d*i){
                System.out.println(i);
                break;
            } n <= d*i n d*i d i {
                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 s = new Scanner(System.in);
        String[] z =s.nextLine().split(" ");
        int n=Integer.parseInt(z[0]);
        int d=Integer.parseInt(z[1])*2+1;
        for(int i=1;i<= 1000;i++){
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        }
    }
} public class Main {
    public static void main(String[] args){
        Scanner s = new Scanner(System.in);
        String[] z =s.nextLine().split(" ");
        int n=Integer.parseInt(z[0]);
        int d=Integer.parseInt(z[1])*2+1;
        for(int i=1;i<= 1000;i++){
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        }
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner s = new Scanner(System.in);
        String[] z =s.nextLine().split(" ");
        int n=Integer.parseInt(z[0]);
        int d=Integer.parseInt(z[1])*2+1;
        for(int i=1;i<= 1000;i++){
            if(n <= d*i){
                System.out.println(i);
                break;
            }
        }
    }
}