import java.util.*;
 
public class Main {
	public static void main (String[] args) {
		Scanner in = new Scanner(System.in);
		
		int N = in.nextInt();
        int D = in.nextInt()*2+1;
        int count = 0;
        
      while(N>0){
        N = N-D;
        count++;
      }
      
      System.out.print(count);
	}
} import java.util.*; util.* java public class Main {
	public static void main (String[] args) {
		Scanner in = new Scanner(System.in);
		
		int N = in.nextInt();
        int D = in.nextInt()*2+1;
        int count = 0;
        
      while(N>0){
        N = N-D;
        count++;
      }
      
      System.out.print(count);
	}
} Main public static void main (String[] args) {
		Scanner in = new Scanner(System.in);
		
		int N = in.nextInt();
        int D = in.nextInt()*2+1;
        int count = 0;
        
      while(N>0){
        N = N-D;
        count++;
      }
      
      System.out.print(count);
	} main {
		Scanner in = new Scanner(System.in);
		
		int N = in.nextInt();
        int D = in.nextInt()*2+1;
        int count = 0;
        
      while(N>0){
        N = N-D;
        count++;
      }
      
      System.out.print(count);
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int N = in.nextInt(); N in.nextInt() in.nextInt in int D = in.nextInt()*2+1; D in.nextInt()*2+1 in.nextInt()*2 in.nextInt() in.nextInt in 2 1 int count = 0; count 0 while(N>0){
        N = N-D;
        count++;
      } N>0 N 0 {
        N = N-D;
        count++;
      } N = N-D N N-D N D count++ count System.out.print(count) System.out.print System.out System System.out count String[] args args public class Main {
	public static void main (String[] args) {
		Scanner in = new Scanner(System.in);
		
		int N = in.nextInt();
        int D = in.nextInt()*2+1;
        int count = 0;
        
      while(N>0){
        N = N-D;
        count++;
      }
      
      System.out.print(count);
	}
} public class Main {
	public static void main (String[] args) {
		Scanner in = new Scanner(System.in);
		
		int N = in.nextInt();
        int D = in.nextInt()*2+1;
        int count = 0;
        
      while(N>0){
        N = N-D;
        count++;
      }
      
      System.out.print(count);
	}
} Main
import java.util.*;
 
public class Main {
	public static void main (String[] args) {
		Scanner in = new Scanner(System.in);
		
		int N = in.nextInt();
        int D = in.nextInt()*2+1;
        int count = 0;
        
      while(N>0){
        N = N-D;
        count++;
      }
      
      System.out.print(count);
	}
}