
import java.util.Scanner;

public 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();
		scan.close();

		System.out.println((Math.min(b, d)-Math.max(a, c)>0)? Math.min(b, d)-Math.max(a, c):"0");

	}
} import java.util.Scanner; Scanner java.util public 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();
		scan.close();

		System.out.println((Math.min(b, d)-Math.max(a, c)>0)? Math.min(b, d)-Math.max(a, c):"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();
		scan.close();

		System.out.println((Math.min(b, d)-Math.max(a, c)>0)? Math.min(b, d)-Math.max(a, c):"0");

	} main {
		Scanner scan = new Scanner(System.in);
		int a = scan.nextInt();
		int b = scan.nextInt();
		int c = scan.nextInt();
		int d = scan.nextInt();
		scan.close();

		System.out.println((Math.min(b, d)-Math.max(a, c)>0)? Math.min(b, d)-Math.max(a, c):"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 scan.close() scan.close scan System.out.println((Math.min(b, d)-Math.max(a, c)>0)? Math.min(b, d)-Math.max(a, c):"0") System.out.println System.out System System.out (Math.min(b, d)-Math.max(a, c)>0)? Math.min(b, d)-Math.max(a, c):"0" (Math.min(b, d)-Math.max(a, c)>0) 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 0 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 "0" String[] args args public 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();
		scan.close();

		System.out.println((Math.min(b, d)-Math.max(a, c)>0)? Math.min(b, d)-Math.max(a, c):"0");

	}
} public 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();
		scan.close();

		System.out.println((Math.min(b, d)-Math.max(a, c)>0)? Math.min(b, d)-Math.max(a, c):"0");

	}
} Main

import java.util.Scanner;

public 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();
		scan.close();

		System.out.println((Math.min(b, d)-Math.max(a, c)>0)? Math.min(b, d)-Math.max(a, c):"0");

	}
}
