64 locomotives of this type were imported from the Soviet Union and the Russian Federation between 1967 and 1995 , numbered in the 내연6xx ( Naeyŏn 6xx ) series .
NUM NOUN ADP DET NOUN AUX VERB ADP DET PROPN PROPN CCONJ DET PROPN PROPN ADP NUM CCONJ NUM , VERB ADP DET PROPN ( PROPN NOUN ) NOUN .