import java.util.*;
import java.math.BigInteger;
 class Main{

     public static void main(String []args){
      Scanner scan = new Scanner(System.in);
      int a = scan.nextInt() ;
      int b =scan.nextInt();
      int c =scan.nextInt();
      int d = scan.nextInt();
      
      int x1 = Math.max(a,c);
      int x2 = Math.min(b,d);
      System.out.println((x2-x1)>0 ? (x2-x1) : 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