embeded if statements alternative-Selecting cell based on a range

HI Guys,

I have a burning question and hate for embedded if statements. Can someone help me with this issue:

I have a tables as below

Period Product
1 A
5 B
15 C
20 D

I have periods one to 20, instead of using embedded if statements is there a simpler way to do this equation?

I want to achieve a final result as below

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
A A A A B B B B B B B B B B C C C C C D

I assumed your period is from positive integral set. 0,5,15,20 are initial limits. 0 is because you need values between: 0-4(A),5-14(B),15-19(C),20-over(D), 99 is because if you step over 20 from definition it will show D letter . The rest hope you know. Match() gives you number of place which will be used in CHOOSE().
Look at MATCH() definition, espacially about match_type.