import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		 Scanner scan = new Scanner(System.in);
	        int N  = scan.nextInt();
	        int D  = scan.nextInt();
	        int i=0;
	        int x =  N;

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

	        for(i=0; x > 0;i++) {
	        	x -= 2*D+1;
	        }
	        System.out.println(String.valueOf(i ));
	}
} Main public static void main(String[] args) {
		 Scanner scan = new Scanner(System.in);
	        int N  = scan.nextInt();
	        int D  = scan.nextInt();
	        int i=0;
	        int x =  N;

	        for(i=0; x > 0;i++) {
	        	x -= 2*D+1;
	        }
	        System.out.println(String.valueOf(i ));
	} main {
		 Scanner scan = new Scanner(System.in);
	        int N  = scan.nextInt();
	        int D  = scan.nextInt();
	        int i=0;
	        int x =  N;

	        for(i=0; x > 0;i++) {
	        	x -= 2*D+1;
	        }
	        System.out.println(String.valueOf(i ));
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int N  = scan.nextInt(); N scan.nextInt() scan.nextInt scan int D  = scan.nextInt(); D scan.nextInt() scan.nextInt scan int i=0; i 0 int x =  N; x N for(i=0; x > 0;i++) {
	        	x -= 2*D+1;
	        } i=0; i=0 i 0 x > 0 x 0 i++ i++ i {
	        	x -= 2*D+1;
	        } {
	        	x -= 2*D+1;
	        } x -= 2*D+1 x 2*D+1 2*D 2 D 1 System.out.println(String.valueOf(i )) System.out.println System.out System System.out String.valueOf(i ) String.valueOf String i String[] args args public class Main {
	public static void main(String[] args) {
		 Scanner scan = new Scanner(System.in);
	        int N  = scan.nextInt();
	        int D  = scan.nextInt();
	        int i=0;
	        int x =  N;

	        for(i=0; x > 0;i++) {
	        	x -= 2*D+1;
	        }
	        System.out.println(String.valueOf(i ));
	}
} public class Main {
	public static void main(String[] args) {
		 Scanner scan = new Scanner(System.in);
	        int N  = scan.nextInt();
	        int D  = scan.nextInt();
	        int i=0;
	        int x =  N;

	        for(i=0; x > 0;i++) {
	        	x -= 2*D+1;
	        }
	        System.out.println(String.valueOf(i ));
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		 Scanner scan = new Scanner(System.in);
	        int N  = scan.nextInt();
	        int D  = scan.nextInt();
	        int i=0;
	        int x =  N;

	        for(i=0; x > 0;i++) {
	        	x -= 2*D+1;
	        }
	        System.out.println(String.valueOf(i ));
	}
}
