SUMIf Unique Values

Hi, I have got a workbook where i need to calculate the total time taken for all users to give a total for the manager. I have wrote the following formula:

=SUMIF(A2:A9,F2,C2:C9)

but this totals all the values including the duplicate times. What i would like is to sumif only the unique values within column c for a unique user. i have attached a sample workbook. Could somebody please help.

Thanks in advance.