import java.util.Scanner;

class Main{
	public static void main(String[] args) {
		Scanner stdIn=new Scanner(System.in);
		int a=stdIn.nextInt(),b=stdIn.nextInt(),c=stdIn.nextInt(),d=stdIn.nextInt();
		if(c>a) a=c;
		if(b>d) b=d;
		if(b-a>0) System.out.print(b-a);
		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