import java.util.*;

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

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