import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D = Integer.parseInt(sc.next());

        int p = 1 + D;
        int count = 0;
        if ( p < N ) {
            count++;
        } else {
            System.out.println(1);
            System.exit(0);
        }
        
        while (p < (N-D)) {
            p += (2*D+1);
            count++;
        }
            
        System.out.println(count);

    }
} import java.util.*; util.* java public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D = Integer.parseInt(sc.next());

        int p = 1 + D;
        int count = 0;
        if ( p < N ) {
            count++;
        } else {
            System.out.println(1);
            System.exit(0);
        }
        
        while (p < (N-D)) {
            p += (2*D+1);
            count++;
        }
            
        System.out.println(count);

    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D = Integer.parseInt(sc.next());

        int p = 1 + D;
        int count = 0;
        if ( p < N ) {
            count++;
        } else {
            System.out.println(1);
            System.exit(0);
        }
        
        while (p < (N-D)) {
            p += (2*D+1);
            count++;
        }
            
        System.out.println(count);

    } main {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D = Integer.parseInt(sc.next());

        int p = 1 + D;
        int count = 0;
        if ( p < N ) {
            count++;
        } else {
            System.out.println(1);
            System.exit(0);
        }
        
        while (p < (N-D)) {
            p += (2*D+1);
            count++;
        }
            
        System.out.println(count);

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = Integer.parseInt(sc.next()); N Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int D = Integer.parseInt(sc.next()); D Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int p = 1 + D; p 1 + D 1 D int count = 0; count 0 if ( p < N ) {
            count++;
        } else {
            System.out.println(1);
            System.exit(0);
        } p < N p N {
            count++;
        } count++ count {
            System.out.println(1);
            System.exit(0);
        } System.out.println(1) System.out.println System.out System System.out 1 System.exit(0) System.exit System 0 while (p < (N-D)) {
            p += (2*D+1);
            count++;
        } p < (N-D) p (N-D) N D {
            p += (2*D+1);
            count++;
        } p += (2*D+1) p (2*D+1) 2*D 2 D 1 count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D = Integer.parseInt(sc.next());

        int p = 1 + D;
        int count = 0;
        if ( p < N ) {
            count++;
        } else {
            System.out.println(1);
            System.exit(0);
        }
        
        while (p < (N-D)) {
            p += (2*D+1);
            count++;
        }
            
        System.out.println(count);

    }
} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D = Integer.parseInt(sc.next());

        int p = 1 + D;
        int count = 0;
        if ( p < N ) {
            count++;
        } else {
            System.out.println(1);
            System.exit(0);
        }
        
        while (p < (N-D)) {
            p += (2*D+1);
            count++;
        }
            
        System.out.println(count);

    }
} Main
import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D = Integer.parseInt(sc.next());

        int p = 1 + D;
        int count = 0;
        if ( p < N ) {
            count++;
        } else {
            System.out.println(1);
            System.exit(0);
        }
        
        while (p < (N-D)) {
            p += (2*D+1);
            count++;
        }
            
        System.out.println(count);

    }
}