import java.util.*;

public class Main {
  public static void main(String[] args) {
    int N, D;
    try(Scanner sc = new Scanner(System.in)) {
      N = sc.nextInt();
      D = sc.nextInt();
    }
    int unit = 2 * D + 1;
    int rest = N % unit;
    int answer = (N - rest)/unit + (rest > 0 ? 1 : 0);
    System.out.println(answer);
  }
} import java.util.*; util.* java public class Main {
  public static void main(String[] args) {
    int N, D;
    try(Scanner sc = new Scanner(System.in)) {
      N = sc.nextInt();
      D = sc.nextInt();
    }
    int unit = 2 * D + 1;
    int rest = N % unit;
    int answer = (N - rest)/unit + (rest > 0 ? 1 : 0);
    System.out.println(answer);
  }
} Main public static void main(String[] args) {
    int N, D;
    try(Scanner sc = new Scanner(System.in)) {
      N = sc.nextInt();
      D = sc.nextInt();
    }
    int unit = 2 * D + 1;
    int rest = N % unit;
    int answer = (N - rest)/unit + (rest > 0 ? 1 : 0);
    System.out.println(answer);
  } main {
    int N, D;
    try(Scanner sc = new Scanner(System.in)) {
      N = sc.nextInt();
      D = sc.nextInt();
    }
    int unit = 2 * D + 1;
    int rest = N % unit;
    int answer = (N - rest)/unit + (rest > 0 ? 1 : 0);
    System.out.println(answer);
  } int N N D; D try(Scanner sc = new Scanner(System.in)) {
      N = sc.nextInt();
      D = sc.nextInt();
    } {
      N = sc.nextInt();
      D = sc.nextInt();
    } Scanner sc = new Scanner(System.in) Scanner sc = new Scanner(System.in) new Scanner(System.in) N = sc.nextInt() N sc.nextInt() sc.nextInt sc D = sc.nextInt() D sc.nextInt() sc.nextInt sc int unit = 2 * D + 1; unit 2 * D + 1 2 * D 2 D 1 int rest = N % unit; rest N % unit N unit int answer = (N - rest)/unit + (rest > 0 ? 1 : 0); answer (N - rest)/unit + (rest > 0 ? 1 : 0) (N - rest)/unit (N - rest) N rest unit (rest > 0 ? 1 : 0) rest > 0 rest 0 1 0 System.out.println(answer) System.out.println System.out System System.out answer String[] args args public class Main {
  public static void main(String[] args) {
    int N, D;
    try(Scanner sc = new Scanner(System.in)) {
      N = sc.nextInt();
      D = sc.nextInt();
    }
    int unit = 2 * D + 1;
    int rest = N % unit;
    int answer = (N - rest)/unit + (rest > 0 ? 1 : 0);
    System.out.println(answer);
  }
} public class Main {
  public static void main(String[] args) {
    int N, D;
    try(Scanner sc = new Scanner(System.in)) {
      N = sc.nextInt();
      D = sc.nextInt();
    }
    int unit = 2 * D + 1;
    int rest = N % unit;
    int answer = (N - rest)/unit + (rest > 0 ? 1 : 0);
    System.out.println(answer);
  }
} Main
import java.util.*;

public class Main {
  public static void main(String[] args) {
    int N, D;
    try(Scanner sc = new Scanner(System.in)) {
      N = sc.nextInt();
      D = sc.nextInt();
    }
    int unit = 2 * D + 1;
    int rest = N % unit;
    int answer = (N - rest)/unit + (rest > 0 ? 1 : 0);
    System.out.println(answer);
  }
}