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 n=1;
        for(int i =1; i<=20; i++) {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        }
        
        System.out.println( n);
    }
} 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 n=1;
        for(int i =1; i<=20; i++) {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        }
        
        System.out.println( n);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        
        int n=1;
        for(int i =1; i<=20; i++) {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        }
        
        System.out.println( n);
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        
        int n=1;
        for(int i =1; i<=20; i++) {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        }
        
        System.out.println( n);
    } 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 n=1; n 1 for(int i =1; i<=20; i++) {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        } int i =1; int i =1; i 1 i<=20 i 20 i++ i++ i {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        } {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        } if( (2*D+1)*i >= N) {
                n = i;
                break;
            } (2*D+1)*i >= N (2*D+1)*i (2*D+1) 2*D 2 D 1 i N {
                n = i;
                break;
            } n = i n i break; System.out.println( n) System.out.println System.out System System.out n 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 n=1;
        for(int i =1; i<=20; i++) {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        }
        
        System.out.println( n);
    }
} public class Main {
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();

        
        int n=1;
        for(int i =1; i<=20; i++) {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        }
        
        System.out.println( n);
    }
} 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 n=1;
        for(int i =1; i<=20; i++) {
            if( (2*D+1)*i >= N) {
                n = i;
                break;
            }
        }
        
        System.out.println( n);
    }
}
