import java.util.*;
import java.lang.*;

public class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        
        int cnt = 0;
        for (int i = 0; i < n; i += d * 2 + 1) {
            cnt++;
        }
        System.out.println(cnt);
    }
} import java.util.*; util.* java import java.lang.*; lang.* java public class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        
        int cnt = 0;
        for (int i = 0; i < n; i += d * 2 + 1) {
            cnt++;
        }
        System.out.println(cnt);
    }
} Main public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        
        int cnt = 0;
        for (int i = 0; i < n; i += d * 2 + 1) {
            cnt++;
        }
        System.out.println(cnt);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        
        int cnt = 0;
        for (int i = 0; i < n; i += d * 2 + 1) {
            cnt++;
        }
        System.out.println(cnt);
    } 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 cnt = 0; cnt 0 for (int i = 0; i < n; i += d * 2 + 1) {
            cnt++;
        } int i = 0; int i = 0; i 0 i < n i n i += d * 2 + 1 i += d * 2 + 1 i d * 2 + 1 d * 2 d 2 1 {
            cnt++;
        } {
            cnt++;
        } cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt 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 cnt = 0;
        for (int i = 0; i < n; i += d * 2 + 1) {
            cnt++;
        }
        System.out.println(cnt);
    }
} public class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        
        int cnt = 0;
        for (int i = 0; i < n; i += d * 2 + 1) {
            cnt++;
        }
        System.out.println(cnt);
    }
} Main
import java.util.*;
import java.lang.*;

public class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        
        int cnt = 0;
        for (int i = 0; i < n; i += d * 2 + 1) {
            cnt++;
        }
        System.out.println(cnt);
    }
}
