import java.util.Scanner;

public class Main {
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        int cov = D+D+1;
        int ans = N/cov + Math.min(1, N%cov);
        System.out.println(ans);
    }
} import java.util.Scanner; Scanner 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 cov = D+D+1;
        int ans = N/cov + Math.min(1, N%cov);
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        int cov = D+D+1;
        int ans = N/cov + Math.min(1, N%cov);
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        int cov = D+D+1;
        int ans = N/cov + Math.min(1, N%cov);
        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 cov = D+D+1; cov D+D+1 D+D+1 D D 1 int ans = N/cov + Math.min(1, N%cov); ans N/cov + Math.min(1, N%cov) N/cov N cov Math.min(1, N%cov) Math.min Math 1 N%cov N cov 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) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        int cov = D+D+1;
        int ans = N/cov + Math.min(1, N%cov);
        System.out.println(ans);
    }
} public class Main {
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        int cov = D+D+1;
        int ans = N/cov + Math.min(1, N%cov);
        System.out.println(ans);
    }
} Main
import java.util.Scanner;

public class Main {
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        int cov = D+D+1;
        int ans = N/cov + Math.min(1, N%cov);
        System.out.println(ans);
    }
}