Brother It is really a matter of happiness for me that you want to earn by lawful means. after all this life is too short to be a savage and disobedient creature of Lord.
But let me tell you that it is never mandatory to be a part of corruption in any deptt. not even in Police. My dad is a PSP and i know that if you are not interested in earning unlawful, no one will make to do that. In fact people respect you even behind your back for being honest and your officers and subordinates fear you because you are not for sale..
go for any deptt. you like and ear lawful.
Why I am happy about MLC is because why do some people do corruption (save those whose hearts are marked will black and will always do corruption no matter if they are rich) is just to buy a car if they are not provided with one by govt., to rent or buy a house if they are not provided with an official one, to hire servant to help at home... for the above reasons most people do corruption but in MLC you get all this by govt.
All the best for your endeavors and please stick to your ideology no matter how big opportunity pops up to do corruption.