import java.util.Scanner;
public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = Integer.parseInt(sc.next());
        int b = Integer.parseInt(sc.next());
        int c = Integer.parseInt(sc.next());
        int d = Integer.parseInt(sc.next());

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

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

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

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

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

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

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