import java.util.*;

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

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