Checking Range, altering out of bounds, checking result against table

So this is the spreadsheet I'm working on:
Screen Shot 2016-04-11 at 10.48.57.png

I want to be able to have a cell, lets call it "a1" have a numerical value i can control.
I then want to check that number to see if it's a value between 3 and "b2".
If it's within that range, it retains its value.
If it's higher, it becomes "b2".
If it's lower, it becomes 3.
I then want to check the resulting value against this table's column "r". Then get the value of column "s".

For example: I enter 17 into "a1".
It checks the number 17, recognising it isn't below 3 or above "b2".
It then checks column "r" for the number 17.
It then checks across that row to column "s", and tells me it is "30.56%"

Another example: I enter -20 into "a1".
It checks the number -20, recognising it is below 3.
It makes the number 3.
It then checks column "r" for the number 3.
It then checks across that row to column "s", and tells me it is "100.00%"

My question is, what would I need to enter into a cell make this happen?


PS: I'm very new to spreadsheets and functions, bear that in mind with any explanations. And apologies if the title or anything else isn't an accurate description of my problem!

Thanks in advance!