import java.util.*;
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();
      int x = Math.max(a,c);
      int y = Math.min(b,d);
      if(b < c||d < a) System.out.println(0);
      else System.out.println(y-x);
    }
}
/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