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