<prompt> Human: Currently, I can set aside 500 a month for my Roth IRA and want to purchase VTTSX.After two months, I bought 1000 worth of VTTSX. Next month, I will have 500 more. Can I buy 500 more of VTTSX since my account is now worth 1000 or do I have to buy VTTSX in 1000 orders every two months?  <response>: Once you hit the 1000 minimum, you can invest additional funds in increments as small as 1. 