The calculated distance (air line) between Cheongsong gun and Naesŏ is approximately 87 miles respectively 140 kilometers.
By car or train, the actual journey to Naesŏ is certainly longer, as only the direct route (as the crow flies) between Cheongsong gun and Naesŏ has been calculated here.
Air line (approximately)
140 kilometers
76 nautical miles