import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		int N = stdIn.nextInt();
		int D= stdIn.nextInt();
		int ans = 0;
		int cnt = 0;
		cnt = D * 2 + 1;
		ans = N / cnt;
		if(N % cnt == 0){
			System.out.println(ans);
		}
		else{
			System.out.println(ans + 1);
		}
		stdIn.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		int N = stdIn.nextInt();
		int D= stdIn.nextInt();
		int ans = 0;
		int cnt = 0;
		cnt = D * 2 + 1;
		ans = N / cnt;
		if(N % cnt == 0){
			System.out.println(ans);
		}
		else{
			System.out.println(ans + 1);
		}
		stdIn.close();
	}
} Main public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		int N = stdIn.nextInt();
		int D= stdIn.nextInt();
		int ans = 0;
		int cnt = 0;
		cnt = D * 2 + 1;
		ans = N / cnt;
		if(N % cnt == 0){
			System.out.println(ans);
		}
		else{
			System.out.println(ans + 1);
		}
		stdIn.close();
	} main {
		Scanner stdIn = new Scanner(System.in);
		int N = stdIn.nextInt();
		int D= stdIn.nextInt();
		int ans = 0;
		int cnt = 0;
		cnt = D * 2 + 1;
		ans = N / cnt;
		if(N % cnt == 0){
			System.out.println(ans);
		}
		else{
			System.out.println(ans + 1);
		}
		stdIn.close();
	} Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) int N = stdIn.nextInt(); N stdIn.nextInt() stdIn.nextInt stdIn int D= stdIn.nextInt(); D stdIn.nextInt() stdIn.nextInt stdIn int ans = 0; ans 0 int cnt = 0; cnt 0 cnt = D * 2 + 1 cnt D * 2 + 1 D * 2 D 2 1 ans = N / cnt ans N / cnt N cnt if(N % cnt == 0){
			System.out.println(ans);
		}
		else{
			System.out.println(ans + 1);
		} N % cnt == 0 N % cnt N cnt 0 {
			System.out.println(ans);
		} System.out.println(ans) System.out.println System.out System System.out ans {
			System.out.println(ans + 1);
		} System.out.println(ans + 1) System.out.println System.out System System.out ans + 1 ans 1 stdIn.close() stdIn.close stdIn String[] args args public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		int N = stdIn.nextInt();
		int D= stdIn.nextInt();
		int ans = 0;
		int cnt = 0;
		cnt = D * 2 + 1;
		ans = N / cnt;
		if(N % cnt == 0){
			System.out.println(ans);
		}
		else{
			System.out.println(ans + 1);
		}
		stdIn.close();
	}
} public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		int N = stdIn.nextInt();
		int D= stdIn.nextInt();
		int ans = 0;
		int cnt = 0;
		cnt = D * 2 + 1;
		ans = N / cnt;
		if(N % cnt == 0){
			System.out.println(ans);
		}
		else{
			System.out.println(ans + 1);
		}
		stdIn.close();
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		int N = stdIn.nextInt();
		int D= stdIn.nextInt();
		int ans = 0;
		int cnt = 0;
		cnt = D * 2 + 1;
		ans = N / cnt;
		if(N % cnt == 0){
			System.out.println(ans);
		}
		else{
			System.out.println(ans + 1);
		}
		stdIn.close();
	}
}