import java.io.*;
import java.util.*;
 
public class Main {
    public static int MAXN = 1600;
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        PrintWriter out = new PrintWriter(System.out);
        int a=cin.nextInt(),b=cin.nextInt(),c=cin.nextInt(),d=cin.nextInt();
        int ans=0;
        for(int i=a;i<b;i++){
        	if(i>=c&&i<d){
        		ans++;
        	}
        }
        out.println(ans);
        out.flush();
        out.close();
        cin.close();
    }
}
/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