import java.util.Scanner;

class Main{
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		int c = stdIn.nextInt();
		int d = stdIn.nextInt();

		int small = (a > c)? a : c;
		int large = (b < d)? b : d;

		int time = (large > small)? large-small : 0;
		System.out.println(time);
	}
}
/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