import java.util.*;

public class Main {

	public static void main(
			String[] args) {
		Scanner sc = new Scanner(System.in);
		int[] abcd = new int[4];
		for (int i = 0; i < 4; i++) {
			abcd[i] = sc.nextInt();
		}
		int ab = abcd[0] > abcd[2] ? abcd[0] : abcd[2];
		int cd = abcd[1] < abcd[3] ? abcd[1] : abcd[3];
		System.out.println(cd - ab > 0 ? cd - ab : 0);
	}
}

/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