
import java.util.Scanner;

class Main{
	public static void main(String[] ag) {
		Scanner sc=new Scanner(System.in);
		int A=sc.nextInt();
		int B=sc.nextInt();
		int C=sc.nextInt();
		int D=sc.nextInt();

		int res=Math.max(Math.min(B, D)-Math.max(A, C), 0);
		System.out.println(res);
	}
}
/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