import java.util.*;

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