What type of folmula would respond to the following conditions:

IF Any Cell in Column AA= A1 and Any Cell in Column AB =B1 then C1=555
IF Any Cell in Column AA= A2 and Any Cell Column AB =B1 then C1=666

IF Any Cell in Column AA= A1 and Any Cell in Column AB =B2 then C1=444
IF Any Cell in Column AA= A2 and Any Cell in Column AB =B2 then C1=777

help me please?

Alex