import java.nio.file.*;
import java.nio.charset.*;
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 max = Math.max(a, c);
        int min = Math.min(b, d);
        if(min >= max){
            System.out.println(min - max);
        }else{
            System.out.println(0);
        }


    }
} import java.nio.file.*; file.* java.nio import java.nio.charset.*; charset.* java.nio 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 max = Math.max(a, c);
        int min = Math.min(b, d);
        if(min >= max){
            System.out.println(min - max);
        }else{
            System.out.println(0);
        }


    }
} 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 max = Math.max(a, c);
        int min = Math.min(b, d);
        if(min >= max){
            System.out.println(min - max);
        }else{
            System.out.println(0);
        }


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


    }
} 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 max = Math.max(a, c);
        int min = Math.min(b, d);
        if(min >= max){
            System.out.println(min - max);
        }else{
            System.out.println(0);
        }


    }
} Main
import java.nio.file.*;
import java.nio.charset.*;
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 max = Math.max(a, c);
        int min = Math.min(b, d);
        if(min >= max){
            System.out.println(min - max);
        }else{
            System.out.println(0);
        }


    }
}