Getting multiple values instead of single value

Hi,

We have Eqp_Id, Doc_No, Valid_From_Date, Report_Date Rec_Id

                        66      199     6/18/2014        9/30/2014  R1

                        66      200     6/18/2014        9/30/2014  R2

                        66      338     7/28/2014        9/30/2014  R2

                        66      375     8/20/2014        9/30/2014  R2

                        66      376     8/20/2014        9/30/2014  R3

I want output Rec_Id for Maximum Doc_No

I am using two formulaes:

Max_Doc_No: =Max([Doc_N]) Where ([Valid_From_Date] Between([Jan First];[Report_Date]) )

Rec=[Rec_Id] Where ([Doc_No]=[Max_Doc_No])

When I output Eqp_id, Max_Doc_No, I am getting

                              66      376

When I output, Eqp_Id, Rec Max_Doc_No

                             66     R1   199

                            66      R2   375

                            66     R3   376

I want output Eqp_Id Rec_Id

                          66   R3

If I am using formula: [Rec_Id] Where ([Doc_No]=Max([Doc_N]) Where ([Valid_From_Date] Between([Jan First];[Report_Date]) )), I am getting multi value error