import java.util.*;
import java.util.Collections;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int range = sc.nextInt() * 2 + 1;
    int cnt = 0;
    while (true) {
      cnt++;
      N -= range;
      if (N <= 0) {
        break;
      }
    }
    System.out.println(cnt);
  }
} import java.util.*; util.* java import java.util.Collections; Collections java.util public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int range = sc.nextInt() * 2 + 1;
    int cnt = 0;
    while (true) {
      cnt++;
      N -= range;
      if (N <= 0) {
        break;
      }
    }
    System.out.println(cnt);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int range = sc.nextInt() * 2 + 1;
    int cnt = 0;
    while (true) {
      cnt++;
      N -= range;
      if (N <= 0) {
        break;
      }
    }
    System.out.println(cnt);
  } main {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int range = sc.nextInt() * 2 + 1;
    int cnt = 0;
    while (true) {
      cnt++;
      N -= range;
      if (N <= 0) {
        break;
      }
    }
    System.out.println(cnt);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int range = sc.nextInt() * 2 + 1; range sc.nextInt() * 2 + 1 sc.nextInt() * 2 sc.nextInt() sc.nextInt sc 2 1 int cnt = 0; cnt 0 while (true) {
      cnt++;
      N -= range;
      if (N <= 0) {
        break;
      }
    } true {
      cnt++;
      N -= range;
      if (N <= 0) {
        break;
      }
    } cnt++ cnt N -= range N range if (N <= 0) {
        break;
      } N <= 0 N 0 {
        break;
      } break; System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int range = sc.nextInt() * 2 + 1;
    int cnt = 0;
    while (true) {
      cnt++;
      N -= range;
      if (N <= 0) {
        break;
      }
    }
    System.out.println(cnt);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int range = sc.nextInt() * 2 + 1;
    int cnt = 0;
    while (true) {
      cnt++;
      N -= range;
      if (N <= 0) {
        break;
      }
    }
    System.out.println(cnt);
  }
} Main
import java.util.*;
import java.util.Collections;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int range = sc.nextInt() * 2 + 1;
    int cnt = 0;
    while (true) {
      cnt++;
      N -= range;
      if (N <= 0) {
        break;
      }
    }
    System.out.println(cnt);
  }
}
