3 times through with a continuously running clock, do one pull-up the first minute, two pull-ups the second minute, three pull-ups the third minute, continuing as long as you are able.
Begin with strict chest-to-bar pull-ups. Once you fail, start over with strict chin-over-bar pull-ups. Once you fail, start over with kipping chest-to-bar pull-ups.
Use as many sets each minute as needed.