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