I need to look up dept by date and emp #. Please see c15. Thanks

A B C
1 Date Emp # Dept
2 5/1/2007 A1054 Sales
3 6/1/2007 B1074 Prod
4 7/1/2007 C2074 Fin
5 8/1/2007 D1085 Sales
6 9/1/2007 e7805 Fin
7 10/2/2007 f8091 Prod
8 11/2/2007 g9071 Sales
9 12/3/2007 g7081 Prod
10 1/3/2008 h9081 Fin
11 2/3/2008 i70550 Sales
12 3/5/2008 j75520 Sales
13
14 Date Emp # DEPT
15 5/1/2007 A1054 =if(vlookup(A15,a2:c12,3)=b15,c,?
16 6/1/2007 B1074
17 7/1/2007 C2074
18 8/1/2007 D1085
19 9/1/2007 e7805
20 10/2/2007 f8091
21 11/2/2007 g9071
22 12/3/2007 g7081
23 1/3/2008 h9081
24 2/3/2008 i70550
25 3/5/2008 j75520