import java.util.*;
import java.util.Arrays;
import java.util.Set;
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((C>=A)&&(C<=B)){
            System.out.println(Math.min(B,D)-C);
        }else if((A>=C)&&(D>=A)){
            System.out.println(Math.min(B,D)-A);
        }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