import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        for (int i = 0; i < 100000000; i++) {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        }
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        for (int i = 0; i < 100000000; i++) {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        }
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        for (int i = 0; i < 100000000; i++) {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        }
    } main {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        for (int i = 0; i < 100000000; i++) {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        }
    } 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 for (int i = 0; i < 100000000; i++) {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        } int i = 0; int i = 0; i 0 i < 100000000 i 100000000 i++ i++ i {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        } {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        } if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            } (2 * D + 1) * i >= N (2 * D + 1) * i (2 * D + 1) 2 * D 2 D 1 i N {
                System.out.println(i);
                return;
            } System.out.println(i) System.out.println System.out System System.out i return; 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();

        for (int i = 0; i < 100000000; i++) {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        }
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        for (int i = 0; i < 100000000; i++) {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        }
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        for (int i = 0; i < 100000000; i++) {
            if ((2 * D + 1) * i >= N) {
                System.out.println(i);
                return;
            }
        }
    }
}
