import java.util.*;
import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.awt.Point;


public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] s = br.readLine().split(" ");
        int n = Integer.parseInt(s[0]);
        int d = Integer.parseInt(s[1]);
        
        System.out.println(n%(2*d+1)==0?n/(2*d+1):n/(2*d+1)+1);
    }

    
}


 import java.util.*; util.* java import java.io.InputStreamReader; InputStreamReader java.io import java.io.BufferedReader; BufferedReader java.io import java.awt.Point; Point java.awt public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] s = br.readLine().split(" ");
        int n = Integer.parseInt(s[0]);
        int d = Integer.parseInt(s[1]);
        
        System.out.println(n%(2*d+1)==0?n/(2*d+1):n/(2*d+1)+1);
    }

    
} Main public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] s = br.readLine().split(" ");
        int n = Integer.parseInt(s[0]);
        int d = Integer.parseInt(s[1]);
        
        System.out.println(n%(2*d+1)==0?n/(2*d+1):n/(2*d+1)+1);
    } main {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] s = br.readLine().split(" ");
        int n = Integer.parseInt(s[0]);
        int d = Integer.parseInt(s[1]);
        
        System.out.println(n%(2*d+1)==0?n/(2*d+1):n/(2*d+1)+1);
    } BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) String[] s = br.readLine().split(" "); s br.readLine().split(" ") br.readLine().split br.readLine() br.readLine br " " int n = Integer.parseInt(s[0]); n Integer.parseInt(s[0]) Integer.parseInt Integer s[0] s 0 int d = Integer.parseInt(s[1]); d Integer.parseInt(s[1]) Integer.parseInt Integer s[1] s 1 System.out.println(n%(2*d+1)==0?n/(2*d+1):n/(2*d+1)+1) System.out.println System.out System System.out n%(2*d+1)==0?n/(2*d+1):n/(2*d+1)+1 n%(2*d+1)==0 n%(2*d+1) n (2*d+1) 2*d 2 d 1 0 n/(2*d+1) n (2*d+1) 2*d 2 d 1 n/(2*d+1)+1 n/(2*d+1) n (2*d+1) 2*d 2 d 1 1 String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] s = br.readLine().split(" ");
        int n = Integer.parseInt(s[0]);
        int d = Integer.parseInt(s[1]);
        
        System.out.println(n%(2*d+1)==0?n/(2*d+1):n/(2*d+1)+1);
    }

    
} public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] s = br.readLine().split(" ");
        int n = Integer.parseInt(s[0]);
        int d = Integer.parseInt(s[1]);
        
        System.out.println(n%(2*d+1)==0?n/(2*d+1):n/(2*d+1)+1);
    }

    
} Main
import java.util.*;
import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.awt.Point;


public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] s = br.readLine().split(" ");
        int n = Integer.parseInt(s[0]);
        int d = Integer.parseInt(s[1]);
        
        System.out.println(n%(2*d+1)==0?n/(2*d+1):n/(2*d+1)+1);
    }

    
}



