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