import java.util.*;

public class Main{
	
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
  	int a=sc.nextInt(),b=sc.nextInt(),c=sc.nextInt(),d=sc.nextInt();
    if(b>=c&&d>=a){
      System.out.println((int)Math.min(Math.min(b-a,d-a),Math.min(b-c,d-c)));
    }else{
      System.out.println(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