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();
 
   if(B<=C || D<=A)System.out.println(0);
   else if(C<=A&& B<=D) System.out.println(B-A);
   else if(A<=C&& D<=B) System.out.println(D-C);
   else if(A<C&&B>C) System.out.println(B-C);
   else System.out.println(D-A);
 }
}
/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