The calculated distance (air line) between Pyeongchang and Seongnam-si is approximately 69 miles respectively 111 kilometers.
By car or train, the actual journey to Seongnam-si is certainly longer, as only the direct route (as the crow flies) between Pyeongchang and Seongnam-si has been calculated here.
Air line (approximately)
111 kilometers
60 nautical miles