How to count the number of words only using string methods using a more efficient regex

Input data
You will read the text of the email from the keyboard. It can span multiple lines and contains only lowercase letters of the English alphabet and spaces.

Output data
A single integer will be displayed, representing the number of distinct words in the email

limitation
The text does not contain more than 100,000 words, and each word can contain up to 25 characters.

 Input data:
thanks for the list of shopping
Is helpful
thanks

Output data:
7

I must ignore the words that are repeated

What I have tried:

<pre>import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Set;
import java.util.TreeSet;
import java.util.*;
 
    class prog {
    public static void main(String args[] ) throws Exception {
  Set<String> words = new TreeSet<>();

   BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

    String line;
    while((line = reader.readLine()) != null){

        words.addAll(
                Arrays.asList( 
                   line.split(" ") // I need to use another method, not split
                )
        );
    }
        System.out.println(words.size()-1);
    }
    }