Employee Code Generation

Hi friends i need to generate employee code based on his first name(firstletter)
Eg: Manoj-(M) along with this they have to check employee code like 'M%'

it will display

M001
M002

if new added na(Manoj)

Employee Code should be M003

then if Employee code exceeds M999

then code should generate like M9A0-M9A9 then it over na M9AA-M9AZ

continuing M9B0-M9B9 --- M9BA-M9BZ

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M9ZZ-M9ZZ
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