With 4 page frames allocation, on the reduced reference string 061071081091012013014015, the sequence of pages replaced by the NRU page replacement algorithm (after the initial 4 pages are loaded) is _____. Assume the clock ticks are after every 5th reference, and that even numbered pages (pages 0,2,4,6,8, not even locations in the reference string) are read and odd numbered pages (pages 1,3,5,7,9, not odd locations in the reference string) are written. In case of a tie, the page in the lowest numbered page frame is replaced (page frames are filled from lowest to highest number). Your answer must be a sequence like the reduced reference string, so for example the FIFO replacements sequence is 0617809123.