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 count = 0;
		
		int see = 2*d+1;
		
		while(true) {
			if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			}
		}
		
		System.out.println(count);
	}

} 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 count = 0;
		
		int see = 2*d+1;
		
		while(true) {
			if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			}
		}
		
		System.out.println(count);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int count = 0;
		
		int see = 2*d+1;
		
		while(true) {
			if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			}
		}
		
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int count = 0;
		
		int see = 2*d+1;
		
		while(true) {
			if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			}
		}
		
		System.out.println(count);
	} 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 count = 0; count 0 int see = 2*d+1; see 2*d+1 2*d 2 d 1 while(true) {
			if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			}
		} true {
			if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			}
		} if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			} n > 0 n 0 {
				n -= see;
				count++;
			} n -= see n see count++ count {
				break;
			} break; System.out.println(count) System.out.println System.out System System.out count 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 count = 0;
		
		int see = 2*d+1;
		
		while(true) {
			if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			}
		}
		
		System.out.println(count);
	}

} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int count = 0;
		
		int see = 2*d+1;
		
		while(true) {
			if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			}
		}
		
		System.out.println(count);
	}

} 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 count = 0;
		
		int see = 2*d+1;
		
		while(true) {
			if(n > 0) {
				n -= see;
				count++;
			}else {
				break;
			}
		}
		
		System.out.println(count);
	}

}
