import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int a = sc.nextInt(), b = sc.nextInt(), c = sc.nextInt(), d = sc.nextInt();
		int ans = Math.min(b, d) - Math.max(a, c);
		System.out.println(ans > 0 ? ans : 0);

		sc.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int a = sc.nextInt(), b = sc.nextInt(), c = sc.nextInt(), d = sc.nextInt();
		int ans = Math.min(b, d) - Math.max(a, c);
		System.out.println(ans > 0 ? ans : 0);

		sc.close();
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int a = sc.nextInt(), b = sc.nextInt(), c = sc.nextInt(), d = sc.nextInt();
		int ans = Math.min(b, d) - Math.max(a, c);
		System.out.println(ans > 0 ? ans : 0);

		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);

		int a = sc.nextInt(), b = sc.nextInt(), c = sc.nextInt(), d = sc.nextInt();
		int ans = Math.min(b, d) - Math.max(a, c);
		System.out.println(ans > 0 ? ans : 0);

		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt() a sc.nextInt() sc.nextInt sc b = sc.nextInt() b sc.nextInt() sc.nextInt sc c = sc.nextInt() c sc.nextInt() sc.nextInt sc d = sc.nextInt(); d sc.nextInt() sc.nextInt sc int ans = Math.min(b, d) - Math.max(a, c); ans 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 System.out.println(ans > 0 ? ans : 0) System.out.println System.out System System.out ans > 0 ? ans : 0 ans > 0 ans 0 ans 0 sc.close() sc.close sc String[] args args public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int a = sc.nextInt(), b = sc.nextInt(), c = sc.nextInt(), d = sc.nextInt();
		int ans = Math.min(b, d) - Math.max(a, c);
		System.out.println(ans > 0 ? ans : 0);

		sc.close();
	}
} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int a = sc.nextInt(), b = sc.nextInt(), c = sc.nextInt(), d = sc.nextInt();
		int ans = Math.min(b, d) - Math.max(a, c);
		System.out.println(ans > 0 ? ans : 0);

		sc.close();
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int a = sc.nextInt(), b = sc.nextInt(), c = sc.nextInt(), d = sc.nextInt();
		int ans = Math.min(b, d) - Math.max(a, c);
		System.out.println(ans > 0 ? ans : 0);

		sc.close();
	}
}
