Nice! These are more uncommon than their comrades 1, 2, 3, 5, 10, 15 and 20 kopeks - I have never found one of these coins in your typical 20-cent world-coin bucket, although prices are apparently low. 1964 seems to have been the highest year of mintage for the two rarely-seen Soviet high denominations (50k and 1 ruble), but still an excellent catch.