import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int aStart = sc.nextInt();
		int aEnd = sc.nextInt();
		int bStart = sc.nextInt();
		int bEnd = sc.nextInt();
		sc.close();

		int start = aStart > bStart ? aStart : bStart;
		int end = aEnd > bEnd ? bEnd : aEnd;

		int answer = end - start;

		if (aEnd < bStart || bEnd < aStart) {
			System.out.println("0");
		} else {
			System.out.println(answer);
		}

	}

}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz