why is this formula wrong? how can it be fixed?

Valuing a Stream of Cash Flows Suppose we plan to save $500 today, and $1,000 at the end of each of the next two years If we earn a fixed 10% interest rate on our savings, how much will we have three years from today? PV=-500 PMT=-1,000 N=3 I/Y=10 CPT FV=3,975 Incorrect. Why