If you arrived in the US in 2013 on an F1 visa, your 5 years or part years were 2013,2014,2015,2016 and 2017. You are a US resident since January 1, 2018 as you passed the substantial presence test in 2018.
As a resident in 2018, you have the same liability for Social Security and Medicare taxes as US citizens.
https://www.irs.gov/individuals/international-taxpayers/foreign-student-liability-for-social-securit...
https://www.irs.gov/individuals/international-taxpayers/alien-residency-examples
