import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N=sc.nextInt(),D=sc.nextInt();
		int ans=1;

		while(true) {
			if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			}
		}
		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(),D=sc.nextInt();
		int ans=1;

		while(true) {
			if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			}
		}
		System.out.println(ans);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N=sc.nextInt(),D=sc.nextInt();
		int ans=1;

		while(true) {
			if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			}
		}
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int N=sc.nextInt(),D=sc.nextInt();
		int ans=1;

		while(true) {
			if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			}
		}
		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 D=sc.nextInt(); D sc.nextInt() sc.nextInt sc int ans=1; ans 1 while(true) {
			if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			}
		} true {
			if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			}
		} if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			} (2*D+1)<N (2*D+1) 2*D 2 D 1 N {
				ans++;
				N-=2*D+1;
			} ans++ ans N-=2*D+1 N 2*D+1 2*D 2 D 1 {
				break;
			} break; 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(),D=sc.nextInt();
		int ans=1;

		while(true) {
			if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			}
		}
		System.out.println(ans);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N=sc.nextInt(),D=sc.nextInt();
		int ans=1;

		while(true) {
			if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			}
		}
		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(),D=sc.nextInt();
		int ans=1;

		while(true) {
			if((2*D+1)<N) {
				ans++;
				N-=2*D+1;
			}else {
				break;
			}
		}
		System.out.println(ans);
	}
}