import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
      int D = sc.nextInt();
      
      System.out.println((int)Math.ceil(N/(2.0*D+1)));
    }
  
  private static long lcm(long m, long n) {
    return m * n / gcd(m, n);
}
  
  private static long gcd(long m, long n) {
    if(m < n) return gcd(n, m);
    if(n == 0) return m;
    return gcd(n, m % n);
}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
      int D = sc.nextInt();
      
      System.out.println((int)Math.ceil(N/(2.0*D+1)));
    }
  
  private static long lcm(long m, long n) {
    return m * n / gcd(m, n);
}
  
  private static long gcd(long m, long n) {
    if(m < n) return gcd(n, m);
    if(n == 0) return m;
    return gcd(n, m % n);
}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
      int D = sc.nextInt();
      
      System.out.println((int)Math.ceil(N/(2.0*D+1)));
    } main {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
      int D = sc.nextInt();
      
      System.out.println((int)Math.ceil(N/(2.0*D+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 System.out.println((int)Math.ceil(N/(2.0*D+1))) System.out.println System.out System System.out (int)Math.ceil(N/(2.0*D+1)) Math.ceil Math N/(2.0*D+1) N (2.0*D+1) 2.0*D 2.0 D 1 String[] args args private static long lcm(long m, long n) {
    return m * n / gcd(m, n);
} lcm {
    return m * n / gcd(m, n);
} return m * n / gcd(m, n); m * n / gcd(m, n) m * n m n gcd(m, n) gcd m n long m m long n n private static long gcd(long m, long n) {
    if(m < n) return gcd(n, m);
    if(n == 0) return m;
    return gcd(n, m % n);
} gcd {
    if(m < n) return gcd(n, m);
    if(n == 0) return m;
    return gcd(n, m % n);
} if(m < n) return gcd(n, m); m < n m n return gcd(n, m); gcd(n, m) gcd n m if(n == 0) return m; n == 0 n 0 return m; m return gcd(n, m % n); gcd(n, m % n) gcd n m % n m n long m m long n n public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
      int D = sc.nextInt();
      
      System.out.println((int)Math.ceil(N/(2.0*D+1)));
    }
  
  private static long lcm(long m, long n) {
    return m * n / gcd(m, n);
}
  
  private static long gcd(long m, long n) {
    if(m < n) return gcd(n, m);
    if(n == 0) return m;
    return gcd(n, m % n);
}
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
      int D = sc.nextInt();
      
      System.out.println((int)Math.ceil(N/(2.0*D+1)));
    }
  
  private static long lcm(long m, long n) {
    return m * n / gcd(m, n);
}
  
  private static long gcd(long m, long n) {
    if(m < n) return gcd(n, m);
    if(n == 0) return m;
    return gcd(n, m % n);
}
} Main
import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
      int D = sc.nextInt();
      
      System.out.println((int)Math.ceil(N/(2.0*D+1)));
    }
  
  private static long lcm(long m, long n) {
    return m * n / gcd(m, n);
}
  
  private static long gcd(long m, long n) {
    if(m < n) return gcd(n, m);
    if(n == 0) return m;
    return gcd(n, m % n);
}
}