Google Sheet Formula: Preventing the serial number of duplicates below to go up (Using Countif)

[omcsarayar]

I'm currently struggling to assign serial number to a series of dynamic data in google spreadsheet.

for example, i have this table below

Product	Serial Number
Apple	1
Orange	1
Lemon	1
Banana	1
Apple	2
Melon	1
Lemon	2
Orange	2
Banana	2
Apple	3

currently on column B i'm using the formula

=COUNTIF($A$1:A1,A1)

But the problem is, when i change the product on column A to another, the serial number of the duplicates below will automatically go up. for instance, if i change the 2nd Apple to Orange, the serial number of the last apple will automatically go up to 2.

i'd like the serial number of duplicates below to not be changed because it will be sent to the customer (i hope i'm making sense).

is there a way for me to do this?
any help will be much appreciated.