import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            
            String strSplit[] = br.readLine().split(" ");
            int A = Integer.parseInt(strSplit[0]);
            int B = Integer.parseInt(strSplit[1]);
            int C = Integer.parseInt(strSplit[2]);
            int D = Integer.parseInt(strSplit[3]);
            
            int AC = Math.max(A, C);
            int BD = Math.min(B, D);
            
            if(BD > AC){
                System.out.println(BD-AC);
            }else{
                System.out.println("0");
            }
            
        }catch(Exception e){
            
        }
    }
}
/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