import java.util.*;
class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
int D = sc.nextInt();
int s = D+D+1;
int p = N % s;
int f = N - p;
if(p==0){
System.out.println(f/s);
}else{
System.out.println(f/s+1);
}
}
} import java.util.*; util.* java class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
int D = sc.nextInt();
int s = D+D+1;
int p = N % s;
int f = N - p;
if(p==0){
System.out.println(f/s);
}else{
System.out.println(f/s+1);
}
}
} Main public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
int D = sc.nextInt();
int s = D+D+1;
int p = N % s;
int f = N - p;
if(p==0){
System.out.println(f/s);
}else{
System.out.println(f/s+1);
}
} main {
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
int D = sc.nextInt();
int s = D+D+1;
int p = N % s;
int f = N - p;
if(p==0){
System.out.println(f/s);
}else{
System.out.println(f/s+1);
}
} 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 s = D+D+1; s D+D+1 D+D+1 D D 1 int p = N % s; p N % s N s int f = N - p; f N - p N p if(p==0){
System.out.println(f/s);
}else{
System.out.println(f/s+1);
} p==0 p 0 {
System.out.println(f/s);
} System.out.println(f/s) System.out.println System.out System System.out f/s f s {
System.out.println(f/s+1);
} System.out.println(f/s+1) System.out.println System.out System System.out f/s+1 f/s f s 1 String[] args args
import java.util.*;
class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
int D = sc.nextInt();
int s = D+D+1;
int p = N % s;
int f = N - p;
if(p==0){
System.out.println(f/s);
}else{
System.out.println(f/s+1);
}
}
}