Number is prime or not?

public class Main {

    public static void main(String[] args) {
        int num = 33, i = 2;
        boolean flag = false;
        while (i <= num / 2) {
            // condition for nonprime number
            if (num % i == 0) {
                flag = true;
                break;
            }

            ++i;
        }

        if (!flag)
            System.out.println(num + " is a prime number.");
        else
            System.out.println(num + " is not a prime number.");
    }
}

33 is not a prime number.