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();
      int x = Math.max(a,c);
      int y = Math.min(b,d);
      if(b < c||d < a) System.out.println(0);
      else System.out.println(y-x);
    }
} 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();
      int x = Math.max(a,c);
      int y = Math.min(b,d);
      if(b < c||d < a) System.out.println(0);
      else System.out.println(y-x);
    }
} 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();
      int x = Math.max(a,c);
      int y = Math.min(b,d);
      if(b < c||d < a) System.out.println(0);
      else System.out.println(y-x);
    } main {
    	Scanner sc= new Scanner(System.in);
      int a = sc.nextInt();
      int b = sc.nextInt();
      int c = sc.nextInt();
      int d = sc.nextInt();
      int x = Math.max(a,c);
      int y = Math.min(b,d);
      if(b < c||d < a) System.out.println(0);
      else System.out.println(y-x);
    } 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 int x = Math.max(a,c); x Math.max(a,c) Math.max Math a c int y = Math.min(b,d); y Math.min(b,d) Math.min Math b d if(b < c||d < a) System.out.println(0);
      else System.out.println(y-x); b < c||d < a b < c b c d < a d a System.out.println(0) System.out.println System.out System System.out 0 System.out.println(y-x) System.out.println System.out System System.out y-x y x 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();
      int x = Math.max(a,c);
      int y = Math.min(b,d);
      if(b < c||d < a) System.out.println(0);
      else System.out.println(y-x);
    }
} 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();
      int x = Math.max(a,c);
      int y = Math.min(b,d);
      if(b < c||d < a) System.out.println(0);
      else System.out.println(y-x);
    }
} 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();
      int x = Math.max(a,c);
      int y = Math.min(b,d);
      if(b < c||d < a) System.out.println(0);
      else System.out.println(y-x);
    }
}