If this is a governmental company they have a pay grade scale for each and every position they offer, which comes with an alloted salary and benefits for that grade. Also if it is government they should send you an offer letter for your acceptance. You can negotiate the salary portion but not the benefits (generally as this is fixed but a graded salary has degrees).

Dont tell them what you expect, ask them what they offer then ask for advice. Salaries even in government can vary a great deal.