You will stop being exempt from January 1st, 2018. Therefore, you are a resident on your 2018 taxes.
This is why:
As IRS gives F-visa students a five-year lifetime exemption, you can only use your exemption for five years lifetime including any exempt visa you were granted before. Since you are given a J -visa for one year (2013), you can only be exempt for four years (2014-2017) while on the F- visa. Your exemption stop in 2017. If you stay more than 183 days starting from January 1st, 2018, you are a resident.
