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 time = 0;

	 	if(Math.max(A,C) <= Math.min(B,D)) {
	 		time = Math.min(B,D) - Math.max(A,C);
	 	}

	 	System.out.println(time);
	 }
} 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 time = 0;

	 	if(Math.max(A,C) <= Math.min(B,D)) {
	 		time = Math.min(B,D) - Math.max(A,C);
	 	}

	 	System.out.println(time);
	 }
} 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 time = 0;

	 	if(Math.max(A,C) <= Math.min(B,D)) {
	 		time = Math.min(B,D) - Math.max(A,C);
	 	}

	 	System.out.println(time);
	 } main {
	 	Scanner sc = new Scanner(System.in);
	 	int A = sc.nextInt();
	 	int B = sc.nextInt();
	 	int C = sc.nextInt();
	 	int D = sc.nextInt();
	 	int time = 0;

	 	if(Math.max(A,C) <= Math.min(B,D)) {
	 		time = Math.min(B,D) - Math.max(A,C);
	 	}

	 	System.out.println(time);
	 } 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 time = 0; time 0 if(Math.max(A,C) <= Math.min(B,D)) {
	 		time = Math.min(B,D) - Math.max(A,C);
	 	} Math.max(A,C) <= Math.min(B,D) Math.max(A,C) Math.max Math A C Math.min(B,D) Math.min Math B D {
	 		time = Math.min(B,D) - Math.max(A,C);
	 	} time = Math.min(B,D) - Math.max(A,C) time 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(time) System.out.println System.out System System.out time 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 time = 0;

	 	if(Math.max(A,C) <= Math.min(B,D)) {
	 		time = Math.min(B,D) - Math.max(A,C);
	 	}

	 	System.out.println(time);
	 }
} 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 time = 0;

	 	if(Math.max(A,C) <= Math.min(B,D)) {
	 		time = Math.min(B,D) - Math.max(A,C);
	 	}

	 	System.out.println(time);
	 }
} 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();
	 	int time = 0;

	 	if(Math.max(A,C) <= Math.min(B,D)) {
	 		time = Math.min(B,D) - Math.max(A,C);
	 	}

	 	System.out.println(time);
	 }
}
