import java.util.*;
public class Main{
public static void main(String[]args){
Scanner sc=new Scanner(System.in);
  int a=sc.nextInt();
  int b=sc.nextInt();
  int c=sc.nextInt();
  int d=sc.nextInt();
  System.out.println((Math.min(b,d)-Math.max(a,c)<0)?0:Math.min(b,d)-Math.max(a,c));
}
} import java.util.*; util.* java public class Main{
public static void main(String[]args){
Scanner sc=new Scanner(System.in);
  int a=sc.nextInt();
  int b=sc.nextInt();
  int c=sc.nextInt();
  int d=sc.nextInt();
  System.out.println((Math.min(b,d)-Math.max(a,c)<0)?0:Math.min(b,d)-Math.max(a,c));
}
} Main public static void main(String[]args){
Scanner sc=new Scanner(System.in);
  int a=sc.nextInt();
  int b=sc.nextInt();
  int c=sc.nextInt();
  int d=sc.nextInt();
  System.out.println((Math.min(b,d)-Math.max(a,c)<0)?0:Math.min(b,d)-Math.max(a,c));
} main {
Scanner sc=new Scanner(System.in);
  int a=sc.nextInt();
  int b=sc.nextInt();
  int c=sc.nextInt();
  int d=sc.nextInt();
  System.out.println((Math.min(b,d)-Math.max(a,c)<0)?0:Math.min(b,d)-Math.max(a,c));
} Scanner sc=new Scanner(System.in); sc new Scanner(System.in) int a=sc.nextInt(); a sc.nextInt() sc.nextInt sc int b=sc.nextInt(); b sc.nextInt() sc.nextInt sc int c=sc.nextInt(); c sc.nextInt() sc.nextInt sc int d=sc.nextInt(); d sc.nextInt() sc.nextInt sc System.out.println((Math.min(b,d)-Math.max(a,c)<0)?0:Math.min(b,d)-Math.max(a,c)) System.out.println System.out System System.out (Math.min(b,d)-Math.max(a,c)<0)?0:Math.min(b,d)-Math.max(a,c) (Math.min(b,d)-Math.max(a,c)<0) Math.min(b,d)-Math.max(a,c) Math.min(b,d) Math.min Math b d Math.max(a,c) Math.max Math a c 0 0 Math.min(b,d)-Math.max(a,c) Math.min(b,d) Math.min Math b d Math.max(a,c) Math.max Math a c String[]args args public class Main{
public static void main(String[]args){
Scanner sc=new Scanner(System.in);
  int a=sc.nextInt();
  int b=sc.nextInt();
  int c=sc.nextInt();
  int d=sc.nextInt();
  System.out.println((Math.min(b,d)-Math.max(a,c)<0)?0:Math.min(b,d)-Math.max(a,c));
}
} public class Main{
public static void main(String[]args){
Scanner sc=new Scanner(System.in);
  int a=sc.nextInt();
  int b=sc.nextInt();
  int c=sc.nextInt();
  int d=sc.nextInt();
  System.out.println((Math.min(b,d)-Math.max(a,c)<0)?0:Math.min(b,d)-Math.max(a,c));
}
} Main
import java.util.*;
public class Main{
public static void main(String[]args){
Scanner sc=new Scanner(System.in);
  int a=sc.nextInt();
  int b=sc.nextInt();
  int c=sc.nextInt();
  int d=sc.nextInt();
  System.out.println((Math.min(b,d)-Math.max(a,c)<0)?0:Math.min(b,d)-Math.max(a,c));
}
}