import java.util.*;

public class Main {
    static long mod = 1000000007;

    public static long gcd(long a, long b) {
        if (a == 0) {
            return b;
        } else if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();

        if (n % (2 * d + 1) == 0) {
            System.out.println(n / (2 * d + 1));
        } else {
            System.out.println(n / (2 * d + 1) + 1);
        }
    }
} import java.util.*; util.* java public class Main {
    static long mod = 1000000007;

    public static long gcd(long a, long b) {
        if (a == 0) {
            return b;
        } else if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();

        if (n % (2 * d + 1) == 0) {
            System.out.println(n / (2 * d + 1));
        } else {
            System.out.println(n / (2 * d + 1) + 1);
        }
    }
} Main static long mod = 1000000007; mod 1000000007 public static long gcd(long a, long b) {
        if (a == 0) {
            return b;
        } else if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        }
    } gcd {
        if (a == 0) {
            return b;
        } else if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        }
    } if (a == 0) {
            return b;
        } else if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        } a == 0 a 0 {
            return b;
        } return b; b if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        } b == 0 b 0 {
            return a;
        } return a; a {
            return gcd(b, a % b);
        } return gcd(b, a % b); gcd(b, a % b) gcd b a % b a b long a a long b b public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();

        if (n % (2 * d + 1) == 0) {
            System.out.println(n / (2 * d + 1));
        } else {
            System.out.println(n / (2 * d + 1) + 1);
        }
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();

        if (n % (2 * d + 1) == 0) {
            System.out.println(n / (2 * d + 1));
        } else {
            System.out.println(n / (2 * d + 1) + 1);
        }
    } 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 if (n % (2 * d + 1) == 0) {
            System.out.println(n / (2 * d + 1));
        } else {
            System.out.println(n / (2 * d + 1) + 1);
        } n % (2 * d + 1) == 0 n % (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 0 {
            System.out.println(n / (2 * d + 1));
        } System.out.println(n / (2 * d + 1)) System.out.println System.out System System.out n / (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 {
            System.out.println(n / (2 * d + 1) + 1);
        } System.out.println(n / (2 * d + 1) + 1) System.out.println System.out System System.out n / (2 * d + 1) + 1 n / (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 1 String[] args args public class Main {
    static long mod = 1000000007;

    public static long gcd(long a, long b) {
        if (a == 0) {
            return b;
        } else if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();

        if (n % (2 * d + 1) == 0) {
            System.out.println(n / (2 * d + 1));
        } else {
            System.out.println(n / (2 * d + 1) + 1);
        }
    }
} public class Main {
    static long mod = 1000000007;

    public static long gcd(long a, long b) {
        if (a == 0) {
            return b;
        } else if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();

        if (n % (2 * d + 1) == 0) {
            System.out.println(n / (2 * d + 1));
        } else {
            System.out.println(n / (2 * d + 1) + 1);
        }
    }
} Main
import java.util.*;

public class Main {
    static long mod = 1000000007;

    public static long gcd(long a, long b) {
        if (a == 0) {
            return b;
        } else if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();

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