
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Integer n = scanner.nextInt();
        Integer d = scanner.nextInt();
        
        int result = 1;
        while(true) {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        }
    }
    
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Integer n = scanner.nextInt();
        Integer d = scanner.nextInt();
        
        int result = 1;
        while(true) {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        }
    }
    
} Main public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Integer n = scanner.nextInt();
        Integer d = scanner.nextInt();
        
        int result = 1;
        while(true) {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        }
    } main {
        Scanner scanner = new Scanner(System.in);
        Integer n = scanner.nextInt();
        Integer d = scanner.nextInt();
        
        int result = 1;
        while(true) {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        }
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) Integer n = scanner.nextInt(); n scanner.nextInt() scanner.nextInt scanner Integer d = scanner.nextInt(); d scanner.nextInt() scanner.nextInt scanner int result = 1; result 1 while(true) {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        } true {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        } if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          } result * (2 * d +1) >= n result * (2 * d +1) result (2 * d +1) 2 * d 2 d 1 n {
            System.out.println(result);
            return;
          } System.out.println(result) System.out.println System.out System System.out result return; result++ result String[] args args public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Integer n = scanner.nextInt();
        Integer d = scanner.nextInt();
        
        int result = 1;
        while(true) {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        }
    }
    
} public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Integer n = scanner.nextInt();
        Integer d = scanner.nextInt();
        
        int result = 1;
        while(true) {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        }
    }
    
} Main

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Integer n = scanner.nextInt();
        Integer d = scanner.nextInt();
        
        int result = 1;
        while(true) {
          if(result * (2 * d +1) >= n) {
            System.out.println(result);
            return;
          }
          result++;
        }
    }
    
}
