import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String[] s1 = sc.nextLine().split(" ");
        int n = Integer.parseInt(s1[0]);
        int d = Integer.parseInt(s1[1]);


        int result=n/(2 * d + 1);

        if (n % (2*d+1) == 0) {
        	result=n/(2 * d + 1);
        } else {
        	result=n/(2 * d + 1) +1;
        }

        System.out.println(result);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String[] s1 = sc.nextLine().split(" ");
        int n = Integer.parseInt(s1[0]);
        int d = Integer.parseInt(s1[1]);


        int result=n/(2 * d + 1);

        if (n % (2*d+1) == 0) {
        	result=n/(2 * d + 1);
        } else {
        	result=n/(2 * d + 1) +1;
        }

        System.out.println(result);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String[] s1 = sc.nextLine().split(" ");
        int n = Integer.parseInt(s1[0]);
        int d = Integer.parseInt(s1[1]);


        int result=n/(2 * d + 1);

        if (n % (2*d+1) == 0) {
        	result=n/(2 * d + 1);
        } else {
        	result=n/(2 * d + 1) +1;
        }

        System.out.println(result);
    } main {
        Scanner sc = new Scanner(System.in);
        String[] s1 = sc.nextLine().split(" ");
        int n = Integer.parseInt(s1[0]);
        int d = Integer.parseInt(s1[1]);


        int result=n/(2 * d + 1);

        if (n % (2*d+1) == 0) {
        	result=n/(2 * d + 1);
        } else {
        	result=n/(2 * d + 1) +1;
        }

        System.out.println(result);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String[] s1 = sc.nextLine().split(" "); s1 sc.nextLine().split(" ") sc.nextLine().split sc.nextLine() sc.nextLine sc " " int n = Integer.parseInt(s1[0]); n Integer.parseInt(s1[0]) Integer.parseInt Integer s1[0] s1 0 int d = Integer.parseInt(s1[1]); d Integer.parseInt(s1[1]) Integer.parseInt Integer s1[1] s1 1 int result=n/(2 * d + 1); result n/(2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 if (n % (2*d+1) == 0) {
        	result=n/(2 * d + 1);
        } else {
        	result=n/(2 * d + 1) +1;
        } n % (2*d+1) == 0 n % (2*d+1) n (2*d+1) 2*d 2 d 1 0 {
        	result=n/(2 * d + 1);
        } result=n/(2 * d + 1) result n/(2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 {
        	result=n/(2 * d + 1) +1;
        } result=n/(2 * d + 1) +1 result n/(2 * d + 1) +1 n/(2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 1 System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String[] s1 = sc.nextLine().split(" ");
        int n = Integer.parseInt(s1[0]);
        int d = Integer.parseInt(s1[1]);


        int result=n/(2 * d + 1);

        if (n % (2*d+1) == 0) {
        	result=n/(2 * d + 1);
        } else {
        	result=n/(2 * d + 1) +1;
        }

        System.out.println(result);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String[] s1 = sc.nextLine().split(" ");
        int n = Integer.parseInt(s1[0]);
        int d = Integer.parseInt(s1[1]);


        int result=n/(2 * d + 1);

        if (n % (2*d+1) == 0) {
        	result=n/(2 * d + 1);
        } else {
        	result=n/(2 * d + 1) +1;
        }

        System.out.println(result);
    }
} Main
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String[] s1 = sc.nextLine().split(" ");
        int n = Integer.parseInt(s1[0]);
        int d = Integer.parseInt(s1[1]);


        int result=n/(2 * d + 1);

        if (n % (2*d+1) == 0) {
        	result=n/(2 * d + 1);
        } else {
        	result=n/(2 * d + 1) +1;
        }

        System.out.println(result);
    }
}
