import java.util.*;
import java.math.BigInteger;
 class Main{

     public static void main(String []args){
      Scanner scan = new Scanner(System.in);
      int a = scan.nextInt() ;
      int b =scan.nextInt();
      int c =scan.nextInt();
      int d = scan.nextInt();
      
      int x1 = Math.max(a,c);
      int x2 = Math.min(b,d);
      System.out.println((x2-x1)>0 ? (x2-x1) : 0) ;
    }
} import java.util.*; util.* java import java.math.BigInteger; BigInteger java.math class Main{

     public static void main(String []args){
      Scanner scan = new Scanner(System.in);
      int a = scan.nextInt() ;
      int b =scan.nextInt();
      int c =scan.nextInt();
      int d = scan.nextInt();
      
      int x1 = Math.max(a,c);
      int x2 = Math.min(b,d);
      System.out.println((x2-x1)>0 ? (x2-x1) : 0) ;
    }
} Main public static void main(String []args){
      Scanner scan = new Scanner(System.in);
      int a = scan.nextInt() ;
      int b =scan.nextInt();
      int c =scan.nextInt();
      int d = scan.nextInt();
      
      int x1 = Math.max(a,c);
      int x2 = Math.min(b,d);
      System.out.println((x2-x1)>0 ? (x2-x1) : 0) ;
    } main {
      Scanner scan = new Scanner(System.in);
      int a = scan.nextInt() ;
      int b =scan.nextInt();
      int c =scan.nextInt();
      int d = scan.nextInt();
      
      int x1 = Math.max(a,c);
      int x2 = Math.min(b,d);
      System.out.println((x2-x1)>0 ? (x2-x1) : 0) ;
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int a = scan.nextInt() ; a scan.nextInt() scan.nextInt scan int b =scan.nextInt(); b scan.nextInt() scan.nextInt scan int c =scan.nextInt(); c scan.nextInt() scan.nextInt scan int d = scan.nextInt(); d scan.nextInt() scan.nextInt scan int x1 = Math.max(a,c); x1 Math.max(a,c) Math.max Math a c int x2 = Math.min(b,d); x2 Math.min(b,d) Math.min Math b d System.out.println((x2-x1)>0 ? (x2-x1) : 0) System.out.println System.out System System.out (x2-x1)>0 ? (x2-x1) : 0 (x2-x1)>0 (x2-x1) x2 x1 0 (x2-x1) x2 x1 0 String []args args
import java.util.*;
import java.math.BigInteger;
 class Main{

     public static void main(String []args){
      Scanner scan = new Scanner(System.in);
      int a = scan.nextInt() ;
      int b =scan.nextInt();
      int c =scan.nextInt();
      int d = scan.nextInt();
      
      int x1 = Math.max(a,c);
      int x2 = Math.min(b,d);
      System.out.println((x2-x1)>0 ? (x2-x1) : 0) ;
    }
}