import 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 s = Math.max(a, c);
        int e = Math.min(b, d);
        if (e - s >= 0)
            System.out.println(e - s);
        else
            System.out.println(0);
    }
} import java.util.*; util.* java 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 s = Math.max(a, c);
        int e = Math.min(b, d);
        if (e - s >= 0)
            System.out.println(e - s);
        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 s = Math.max(a, c);
        int e = Math.min(b, d);
        if (e - s >= 0)
            System.out.println(e - s);
        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 s = Math.max(a, c);
        int e = Math.min(b, d);
        if (e - s >= 0)
            System.out.println(e - s);
        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 s = Math.max(a, c); s Math.max(a, c) Math.max Math a c int e = Math.min(b, d); e Math.min(b, d) Math.min Math b d if (e - s >= 0)
            System.out.println(e - s);
        else
            System.out.println(0); e - s >= 0 e - s e s 0 System.out.println(e - s) System.out.println System.out System System.out e - s e s 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 s = Math.max(a, c);
        int e = Math.min(b, d);
        if (e - s >= 0)
            System.out.println(e - s);
        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 s = Math.max(a, c);
        int e = Math.min(b, d);
        if (e - s >= 0)
            System.out.println(e - s);
        else
            System.out.println(0);
    }
} Main
import 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 s = Math.max(a, c);
        int e = Math.min(b, d);
        if (e - s >= 0)
            System.out.println(e - s);
        else
            System.out.println(0);
    }
}
