import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int a = input.nextInt();
        int b = input.nextInt();
        int flag = b * 2 + 1;
        if(a % flag == 0) System.out.println(a / flag);
        else System.out.println(a / flag + 1);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int a = input.nextInt();
        int b = input.nextInt();
        int flag = b * 2 + 1;
        if(a % flag == 0) System.out.println(a / flag);
        else System.out.println(a / flag + 1);
    }
} Main public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int a = input.nextInt();
        int b = input.nextInt();
        int flag = b * 2 + 1;
        if(a % flag == 0) System.out.println(a / flag);
        else System.out.println(a / flag + 1);
    } main {
        Scanner input = new Scanner(System.in);
        int a = input.nextInt();
        int b = input.nextInt();
        int flag = b * 2 + 1;
        if(a % flag == 0) System.out.println(a / flag);
        else System.out.println(a / flag + 1);
    } Scanner input = new Scanner(System.in); input new Scanner(System.in) int a = input.nextInt(); a input.nextInt() input.nextInt input int b = input.nextInt(); b input.nextInt() input.nextInt input int flag = b * 2 + 1; flag b * 2 + 1 b * 2 b 2 1 if(a % flag == 0) System.out.println(a / flag);
        else System.out.println(a / flag + 1); a % flag == 0 a % flag a flag 0 System.out.println(a / flag) System.out.println System.out System System.out a / flag a flag System.out.println(a / flag + 1) System.out.println System.out System System.out a / flag + 1 a / flag a flag 1 String[] args args public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int a = input.nextInt();
        int b = input.nextInt();
        int flag = b * 2 + 1;
        if(a % flag == 0) System.out.println(a / flag);
        else System.out.println(a / flag + 1);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int a = input.nextInt();
        int b = input.nextInt();
        int flag = b * 2 + 1;
        if(a % flag == 0) System.out.println(a / flag);
        else System.out.println(a / flag + 1);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int a = input.nextInt();
        int b = input.nextInt();
        int flag = b * 2 + 1;
        if(a % flag == 0) System.out.println(a / flag);
        else System.out.println(a / flag + 1);
    }
}
