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();

        sc.close();

        int end = Math.min(b, d);
        int start = Math.max(a, c);

        if (end - start > 0) {
            System.out.println(end - 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 = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();

        sc.close();

        int end = Math.min(b, d);
        int start = Math.max(a, c);

        if (end - start > 0) {
            System.out.println(end - start);
        } 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();

        sc.close();

        int end = Math.min(b, d);
        int start = Math.max(a, c);

        if (end - start > 0) {
            System.out.println(end - start);
        } 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();

        sc.close();

        int end = Math.min(b, d);
        int start = Math.max(a, c);

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

        sc.close();

        int end = Math.min(b, d);
        int start = Math.max(a, c);

        if (end - start > 0) {
            System.out.println(end - start);
        } 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();

        sc.close();

        int end = Math.min(b, d);
        int start = Math.max(a, c);

        if (end - start > 0) {
            System.out.println(end - 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 = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();

        sc.close();

        int end = Math.min(b, d);
        int start = Math.max(a, c);

        if (end - start > 0) {
            System.out.println(end - start);
        } else {
            System.out.println(0);
        }
    }
}