import java.util.Scanner;
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();//14
	int d = sc.nextInt();//3
    int result = 0;
    
    if(n == 1 || n == 2){
      System.out.println(1);
    }else{
    for(int i = 0;i < n;i++){
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    }
    System.out.println(result);
    }
  }
} import java.util.Scanner; Scanner java.util class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();//14
	int d = sc.nextInt();//3
    int result = 0;
    
    if(n == 1 || n == 2){
      System.out.println(1);
    }else{
    for(int i = 0;i < n;i++){
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    }
    System.out.println(result);
    }
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();//14
	int d = sc.nextInt();//3
    int result = 0;
    
    if(n == 1 || n == 2){
      System.out.println(1);
    }else{
    for(int i = 0;i < n;i++){
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    }
    System.out.println(result);
    }
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();//14
	int d = sc.nextInt();//3
    int result = 0;
    
    if(n == 1 || n == 2){
      System.out.println(1);
    }else{
    for(int i = 0;i < n;i++){
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    }
    System.out.println(result);
    }
  } 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 result = 0; result 0 if(n == 1 || n == 2){
      System.out.println(1);
    }else{
    for(int i = 0;i < n;i++){
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    }
    System.out.println(result);
    } n == 1 || n == 2 n == 1 n 1 n == 2 n 2 {
      System.out.println(1);
    } System.out.println(1) System.out.println System.out System System.out 1 {
    for(int i = 0;i < n;i++){
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    }
    System.out.println(result);
    } for(int i = 0;i < n;i++){
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    } {
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    } if((2*d+1)*i >= n){
        result = i;
        break;
      } (2*d+1)*i >= n (2*d+1)*i (2*d+1) 2*d 2 d 1 i n {
        result = i;
        break;
      } result = i result i break; System.out.println(result) System.out.println System.out System System.out result String[] args args
import java.util.Scanner;
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();//14
	int d = sc.nextInt();//3
    int result = 0;
    
    if(n == 1 || n == 2){
      System.out.println(1);
    }else{
    for(int i = 0;i < n;i++){
      if((2*d+1)*i >= n){
        result = i;
        break;
      }
    }
    System.out.println(result);
    }
  }
}