import java.util.*;

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

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int a=sc.nextInt(),b=sc.nextInt(),c=sc.nextInt(),d=sc.nextInt();
    int ans=Math.min(b,d)-Math.max(a,c);
    if(ans>0){
      System.out.println(ans);
    }else{
      System.out.println(0);
    }
  }
}