import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
	        int N = sc.nextInt();
	        int D = sc.nextInt();
	        int ans = 0;
	        
	        int D1 = D + D + 1;
	        
	        if(N % D1 == 0){
	          ans = N / D1;
	        } else {
	          ans = N / D1 +1;
	        }
	        
	        System.out.println(ans);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
	        int N = sc.nextInt();
	        int D = sc.nextInt();
	        int ans = 0;
	        
	        int D1 = D + D + 1;
	        
	        if(N % D1 == 0){
	          ans = N / D1;
	        } else {
	          ans = N / D1 +1;
	        }
	        
	        System.out.println(ans);
	}
} Main public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
	        int N = sc.nextInt();
	        int D = sc.nextInt();
	        int ans = 0;
	        
	        int D1 = D + D + 1;
	        
	        if(N % D1 == 0){
	          ans = N / D1;
	        } else {
	          ans = N / D1 +1;
	        }
	        
	        System.out.println(ans);
	} main {
		 Scanner sc = new Scanner(System.in);
	        int N = sc.nextInt();
	        int D = sc.nextInt();
	        int ans = 0;
	        
	        int D1 = D + D + 1;
	        
	        if(N % D1 == 0){
	          ans = N / D1;
	        } else {
	          ans = N / D1 +1;
	        }
	        
	        System.out.println(ans);
	} 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 int ans = 0; ans 0 int D1 = D + D + 1; D1 D + D + 1 D + D + 1 D D 1 if(N % D1 == 0){
	          ans = N / D1;
	        } else {
	          ans = N / D1 +1;
	        } N % D1 == 0 N % D1 N D1 0 {
	          ans = N / D1;
	        } ans = N / D1 ans N / D1 N D1 {
	          ans = N / D1 +1;
	        } ans = N / D1 +1 ans N / D1 +1 N / D1 N D1 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
	        int N = sc.nextInt();
	        int D = sc.nextInt();
	        int ans = 0;
	        
	        int D1 = D + D + 1;
	        
	        if(N % D1 == 0){
	          ans = N / D1;
	        } else {
	          ans = N / D1 +1;
	        }
	        
	        System.out.println(ans);
	}
} public class Main {
	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
	        int N = sc.nextInt();
	        int D = sc.nextInt();
	        int ans = 0;
	        
	        int D1 = D + D + 1;
	        
	        if(N % D1 == 0){
	          ans = N / D1;
	        } else {
	          ans = N / D1 +1;
	        }
	        
	        System.out.println(ans);
	}
} Main
import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		 Scanner sc = new Scanner(System.in);
	        int N = sc.nextInt();
	        int D = sc.nextInt();
	        int ans = 0;
	        
	        int D1 = D + D + 1;
	        
	        if(N % D1 == 0){
	          ans = N / D1;
	        } else {
	          ans = N / D1 +1;
	        }
	        
	        System.out.println(ans);
	}
}