Be like JJG and set a DCA plan into effect.

Pick a dollar amount say 200 a week and buy 200 a week for 200 weeks in a row.

Be sure you can afford to do that.

Also set aside a lump sum to  buy the dip.

ie we are at 17.3k

set aside 15000 for buys at 16k, 14.5k and 12.1k

So the plan above is a plan to invest 40,000 over 200 weeks and as much as 45,000 more in that same time frame.

Obviously do not spent the above amounts if they are unaffordable and that is a real key spend only what you can lose and no more.