Shell Programming and Scripting

Hi,
I need a unix shell script for this requirement and is URGENT
My input text file contains
A-1
B-1
C-1
D-2
E-2
F-3
G-3
H-3
I-3
J-4
K-4
L-5
My expected result should be:
if flag is 1, it has to delete A, B, C
if flag is 2, it has to delete D,E
if flag is 3, it has to delete F,G,H,I
if flag is 4, it has to delete J,K
if flag is 5, it has to delete L
(note: Deletion should happen in parallel and A to L are tables)
Example: if flag=1 then
delete from A
delete from B
delete from C
fi
..................

Code:

echo "Pls input flag"
read flag
echo "Your input is $flag"
egrep -v $flag yourfile