I am a staff at the Ministry of Religious Affairs.
Although you will occasionally find an example of staff as a countable noun, it is extremely rare.
Used as an uncountable noun, staff refers to people who work for a particular organisation:
Used as a countable noun, a staff is a kind of stick with certain features and functions:
In the context of your writing one of these meanings, staff countable / staff uncountable, will probably be more obvious than the other. However, if you want a high score in IELTS for vocabulary, I suggest you choose the most appropriate meaning!
If you really must use a countable noun, you can do this:
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