Automate a suggested value to be entered into a cell

I would like to automate values into cells U30 THRU U600

SUGGESTED SHARES         =ROUNDDOWN(($Y$17-$Y$18)/$Q30,0) 

UNALLOCATED FUNDS    =$Y$17-$Y$18

ADDITIONAL SHARES         U30 thru u600

Using the following macro whenever I manually enter a "suggested share" into u30 thru u600 the "unallocated funds" decrease and the macro generates a message.

Private Sub Worksheet_Change(ByVal Target As Range)

ActiveSheet.Range("$AW$21:$AX$600").AutoFilter Field:=1

If Not (Application.Intersect(Range(" U30:U600"), Target) Is Nothing) Then

If MsgBox("Select 'No' until ADDITIONAL SHARES are manually entered. Have you finished manually entering 'ADDITIONAL SHARES' ?", vbQuestion + vbYesNo, "") = vbYes Then

Call ManualCalculate


End If

End If

End Sub

I would like to automate this manual input with priority given to the lowest to highest cell ie u30 being the lowest.