how much vitamin D

I am 25 year women, i live in minnesota( weather is so cold here) i dont do any job( dont have work visa for usa) stay in home all day ( go out after 6-7 pm that time its all dark outside, no daylight no sun.. how much vitamin d i should take? I am not pragnent . 
Is 1000 iu twice or thrice a week is ok? Anyone can please suggest me?