I am a Green card holder. I came in the United States 2 years ago. I am going back to my country to get married next year. My question is that in order to get the citizenship , I have to have a 3 year days and 5 year period or 5 year days counts only? My intention is to get married and then go and come back here

To be eligible to apply for naturalization, you must be a permanent resident for 5 years and you must be in US no less than 50% of 5 years period...