import java.util.*;
import java.math.*;

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