import java.util.*;

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