import java.util.*;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double d = sc.nextInt()*2+1;
        System.out.println((int)Math.ceil(n/d));
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double d = sc.nextInt()*2+1;
        System.out.println((int)Math.ceil(n/d));
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double d = sc.nextInt()*2+1;
        System.out.println((int)Math.ceil(n/d));
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double d = sc.nextInt()*2+1;
        System.out.println((int)Math.ceil(n/d));
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc double d = sc.nextInt()*2+1; d sc.nextInt()*2+1 sc.nextInt()*2 sc.nextInt() sc.nextInt sc 2 1 System.out.println((int)Math.ceil(n/d)) System.out.println System.out System System.out (int)Math.ceil(n/d) Math.ceil Math n/d n d String[] args args public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double d = sc.nextInt()*2+1;
        System.out.println((int)Math.ceil(n/d));
    }
} public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double d = sc.nextInt()*2+1;
        System.out.println((int)Math.ceil(n/d));
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double d = sc.nextInt()*2+1;
        System.out.println((int)Math.ceil(n/d));
    }
}
