import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class Main {
  public static void main(String[] args)throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int n = Integer.parseInt(str[0]);
    int d = Integer.parseInt(str[1]);
    int watchman = (d*2)+1;
    if(n%watchman != 0)
      System.out.println(n/watchman + 1);
    else
      System.out.println(n/watchman);
  }
} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.IOException; IOException java.io public class Main {
  public static void main(String[] args)throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int n = Integer.parseInt(str[0]);
    int d = Integer.parseInt(str[1]);
    int watchman = (d*2)+1;
    if(n%watchman != 0)
      System.out.println(n/watchman + 1);
    else
      System.out.println(n/watchman);
  }
} Main public static void main(String[] args)throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int n = Integer.parseInt(str[0]);
    int d = Integer.parseInt(str[1]);
    int watchman = (d*2)+1;
    if(n%watchman != 0)
      System.out.println(n/watchman + 1);
    else
      System.out.println(n/watchman);
  } main {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int n = Integer.parseInt(str[0]);
    int d = Integer.parseInt(str[1]);
    int watchman = (d*2)+1;
    if(n%watchman != 0)
      System.out.println(n/watchman + 1);
    else
      System.out.println(n/watchman);
  } BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); in new BufferedReader(new InputStreamReader(System.in)) String[] str = in.readLine().split(" "); str in.readLine().split(" ") in.readLine().split in.readLine() in.readLine in " " int n = Integer.parseInt(str[0]); n Integer.parseInt(str[0]) Integer.parseInt Integer str[0] str 0 int d = Integer.parseInt(str[1]); d Integer.parseInt(str[1]) Integer.parseInt Integer str[1] str 1 int watchman = (d*2)+1; watchman (d*2)+1 (d*2) d 2 1 if(n%watchman != 0)
      System.out.println(n/watchman + 1);
    else
      System.out.println(n/watchman); n%watchman != 0 n%watchman n watchman 0 System.out.println(n/watchman + 1) System.out.println System.out System System.out n/watchman + 1 n/watchman n watchman 1 System.out.println(n/watchman) System.out.println System.out System System.out n/watchman n watchman String[] args args public class Main {
  public static void main(String[] args)throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int n = Integer.parseInt(str[0]);
    int d = Integer.parseInt(str[1]);
    int watchman = (d*2)+1;
    if(n%watchman != 0)
      System.out.println(n/watchman + 1);
    else
      System.out.println(n/watchman);
  }
} public class Main {
  public static void main(String[] args)throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int n = Integer.parseInt(str[0]);
    int d = Integer.parseInt(str[1]);
    int watchman = (d*2)+1;
    if(n%watchman != 0)
      System.out.println(n/watchman + 1);
    else
      System.out.println(n/watchman);
  }
} Main
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class Main {
  public static void main(String[] args)throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String[] str = in.readLine().split(" ");
    int n = Integer.parseInt(str[0]);
    int d = Integer.parseInt(str[1]);
    int watchman = (d*2)+1;
    if(n%watchman != 0)
      System.out.println(n/watchman + 1);
    else
      System.out.println(n/watchman);
  }
}