four: 24 wallclock secs (20.96 usr +  2.30 sys = 23.26 CPU)
  one: 30 wallclock secs (28.59 usr +  1.79 sys = 30.38 CPU)
three: 22 wallclock secs (19.01 usr +  2.29 sys = 21.30 CPU)
  two: 15 wallclock secs (13.54 usr +  1.72 sys = 15.26 CPU)