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();
        int ans = 0;

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

        System.out.println(ans);

        sc.close();
    }    
} 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();
        int ans = 0;

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

        System.out.println(ans);

        sc.close();
    }    
} Main public static void main(String[] args) throws Exception {
        
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;

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

        System.out.println(ans);

        sc.close();
    } main {
        
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        int ans = 0;

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

        System.out.println(ans);

        sc.close();
    } 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 ans = 0; ans 0 if (n % ((d * 2) + 1) == 0) {
            ans = n / ((d * 2) + 1);
        } else {
            ans = n / ((d * 2) + 1) + 1;
        } n % ((d * 2) + 1) == 0 n % ((d * 2) + 1) n ((d * 2) + 1) (d * 2) d 2 1 0 {
            ans = n / ((d * 2) + 1);
        } ans = n / ((d * 2) + 1) ans n / ((d * 2) + 1) n ((d * 2) + 1) (d * 2) d 2 1 {
            ans = n / ((d * 2) + 1) + 1;
        } ans = n / ((d * 2) + 1) + 1 ans n / ((d * 2) + 1) + 1 n / ((d * 2) + 1) n ((d * 2) + 1) (d * 2) d 2 1 1 System.out.println(ans) System.out.println System.out System System.out ans sc.close() sc.close sc 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();
        int ans = 0;

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

        System.out.println(ans);

        sc.close();
    }    
} 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();
        int ans = 0;

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

        System.out.println(ans);

        sc.close();
    }    
} 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();
        int ans = 0;

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

        System.out.println(ans);

        sc.close();
    }    
}
