import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class Main { 
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split(" ");
		int treeCount = Integer.parseInt(line[0]);
		int canWatch = Integer.parseInt(line[1])*2+1;
		for(int i = 1;i<=20;i++) {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		}
		
		
		
		
	}
} import java.util.ArrayList; ArrayList java.util import java.util.Collections; Collections java.util import java.util.Scanner; Scanner java.util public class Main { 
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split(" ");
		int treeCount = Integer.parseInt(line[0]);
		int canWatch = Integer.parseInt(line[1])*2+1;
		for(int i = 1;i<=20;i++) {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		}
		
		
		
		
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split(" ");
		int treeCount = Integer.parseInt(line[0]);
		int canWatch = Integer.parseInt(line[1])*2+1;
		for(int i = 1;i<=20;i++) {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		}
		
		
		
		
	} main {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split(" ");
		int treeCount = Integer.parseInt(line[0]);
		int canWatch = Integer.parseInt(line[1])*2+1;
		for(int i = 1;i<=20;i++) {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		}
		
		
		
		
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String[] line = sc.nextLine().split(" "); line sc.nextLine().split(" ") sc.nextLine().split sc.nextLine() sc.nextLine sc " " int treeCount = Integer.parseInt(line[0]); treeCount Integer.parseInt(line[0]) Integer.parseInt Integer line[0] line 0 int canWatch = Integer.parseInt(line[1])*2+1; canWatch Integer.parseInt(line[1])*2+1 Integer.parseInt(line[1])*2 Integer.parseInt(line[1]) Integer.parseInt Integer line[1] line 1 2 1 for(int i = 1;i<=20;i++) {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		} int i = 1; int i = 1; i 1 i<=20 i 20 i++ i++ i {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		} {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		} if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			} treeCount <= canWatch*i treeCount canWatch*i canWatch i {
				System.out.println(i);
				break;
			} System.out.println(i) System.out.println System.out System System.out i break; String[] args args public class Main { 
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split(" ");
		int treeCount = Integer.parseInt(line[0]);
		int canWatch = Integer.parseInt(line[1])*2+1;
		for(int i = 1;i<=20;i++) {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		}
		
		
		
		
	}
} public class Main { 
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split(" ");
		int treeCount = Integer.parseInt(line[0]);
		int canWatch = Integer.parseInt(line[1])*2+1;
		for(int i = 1;i<=20;i++) {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		}
		
		
		
		
	}
} Main
import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class Main { 
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] line = sc.nextLine().split(" ");
		int treeCount = Integer.parseInt(line[0]);
		int canWatch = Integer.parseInt(line[1])*2+1;
		for(int i = 1;i<=20;i++) {
			if(treeCount <= canWatch*i) {
				System.out.println(i);
				break;
			}
		}
		
		
		
		
	}
}