
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

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

	}
} import java.util.ArrayList; ArrayList java.util import java.util.List; List java.util 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();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
		int e = Math.max(a, c);
		int f = Math.min(b, d);
		
		if (f >= e) {
			System.out.println(f - e);
		} 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 e = Math.max(a, c);
		int f = Math.min(b, d);
		
		if (f >= e) {
			System.out.println(f - e);
		} 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 e = Math.max(a, c);
		int f = Math.min(b, d);
		
		if (f >= e) {
			System.out.println(f - e);
		} 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 e = Math.max(a, c); e Math.max(a, c) Math.max Math a c int f = Math.min(b, d); f Math.min(b, d) Math.min Math b d if (f >= e) {
			System.out.println(f - e);
		} else {
			System.out.println(0);
		} f >= e f e {
			System.out.println(f - e);
		} System.out.println(f - e) System.out.println System.out System System.out f - e f e {
			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 e = Math.max(a, c);
		int f = Math.min(b, d);
		
		if (f >= e) {
			System.out.println(f - e);
		} 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 e = Math.max(a, c);
		int f = Math.min(b, d);
		
		if (f >= e) {
			System.out.println(f - e);
		} else {
			System.out.println(0);
		}

	}
} Main

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

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

	}
}
