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

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

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