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();
		if(c <= a) {
			int w = a;
			a = c;
			c = w;
			int y = b;
			b = d;
			d = y;
		}
		//これでa<cである
		if(b <= c) {
			System.out.println(0);
			return;
		}
		if(b <= d) {
			System.out.println(b - c);
		} else {
			System.out.println(d - c);
		}
	}
}
/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