What is output?

public class MyEvenNumbers $\{$

public static void main$($String$[]$ args$)\{$

HashSet evenNumbers $=$ new HashSet$()$;

evenNumbers.add$(2)$;

evenNumbers.add$(4)$;

evenNumbers.add$(6)$;

evenNumbers.add$(2)$;

System.out.println$($evenNumbers$.$size$())$;

$\}$

$\}$

Question $45$ options:

$2$

$3$

$4$

$6$