Cyzicus is the mint. I think this gives everything. Constantine II, AE follis. Cyzicus. AD 325-326. CONSTANTINVS IVN NOB C, laureate, draped and cuirassed bust left. PROVIDEN-TIAE CAESS, campgate, seven layers, two turrets, star above, no doors. Mintmark SMK Epsilon dot. RIC VII Cyzicus 37.
I believe it is Constantius II. While I can'y make out the start of the legend, you can clearly see CONSTANTIVSNOBC and a count of the letters confirms it is one short to be CONSTNATINVSNOBC. SC