import java.util.Scanner;

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 count = Math.min(b, d) - Math.max(a, c);
		if (count < 0) {
			System.out.println(0);
		} else {
			System.out.println(count);
		}
	}
} import java.util.Scanner; Scanner java.util 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 count = Math.min(b, d) - Math.max(a, c);
		if (count < 0) {
			System.out.println(0);
		} else {
			System.out.println(count);
		}
	}
} 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 count = Math.min(b, d) - Math.max(a, c);
		if (count < 0) {
			System.out.println(0);
		} else {
			System.out.println(count);
		}
	} main {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		
		int count = Math.min(b, d) - Math.max(a, c);
		if (count < 0) {
			System.out.println(0);
		} else {
			System.out.println(count);
		}
	} 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 count = Math.min(b, d) - Math.max(a, c); count 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 if (count < 0) {
			System.out.println(0);
		} else {
			System.out.println(count);
		} count < 0 count 0 {
			System.out.println(0);
		} System.out.println(0) System.out.println System.out System System.out 0 {
			System.out.println(count);
		} System.out.println(count) System.out.println System.out System System.out count String[] args args
import java.util.Scanner;

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