This is part of a larger chart:

0 1 2 3
0 0 8 6 4
1 9 7 5 3
2 8 6 4 2
3 7 5 3 1
4 6 4 2 0

I am trying to create a calculation wherein someone types a 2 digit
number (on the left below) and the result is a 1 digit number (number
on the right below) based on the above chart. Example:

41 = 4
33 = 1
32 = 3
13 = 3

Several combinations of the 2 digit number will equal the same single
digit number (ie: 32=3 & 13=3, etc.). I want the single digit number
to automatically appear based on the top chart.

I am a basic Excel user and am unsure of of the formula that I can
create. I would appreciate any advice.

Thank you.