I am in need of an IF Function that will check the first three characters in Column B and Set a Text Value in Column A for that row

Example: If Cell B1 = P42ABC123N, Then cell A1 is set to "F32"

IF B1 Begins with P21, Set A1 to F21 or,
If B1 Begins with P24, Set A1 to F24 or,
If B1 Begins with P28, Set A1 to F28 or,
If B1 Begins with P12, Set A1 to F32 or,
If B1 Begins with P32, Set A1 to F32 or,
If B1 Begins with P42, Set A1 to F32 or,
If B1 Begins with P33, Set A1 to S33 or,
If B1 Begins with P46, Set A1 to S46