ABC Analysis "How to create a formula to letter rank cells based on percentages"

I need a formula in column "F" that automaticly determines the ABC Ranking based on the following percentages from column "E"

From the top down...

A=the first 80%
B=the next 14%
C=the next 4%
D=the next 1%
DEAD=all 0%

Basicly the top 80% needs to display "A"
the next 14% should display "B" then 4% "C" and so on...

I have attached a file where I manually entered the Ranking in column "F" to display the desired results. Column