What is the payback period for AMP, Inc.?

AMP, Inc., has invested $2,165,800 on equipment. The firm uses payback period criteria of not accepting any project that takes more than four years to recover costs. The company anticipates cash flows of $ 448,386, $512,178, $561,755, $764,997,$816,500 and $825,375 over the next six years. What is the payback period?