import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt() , b = sc.nextInt(), 
				c = sc.nextInt(), d = sc.nextInt();
		
		if(Math.min(b, d)-Math.max(a, c)>0) {
			System.out.print(Math.min(b, d)-Math.max(a, c));
		}
		else System.out.print("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