to square :n
  output :n * :n
end
to trial :r
  output less? sum square random :r square random :r  square :r
end
to sim :n :r
  make "hits 0
  repeat :n [if trial :r [make "hits :hits + 1]]
  output 4 * :hits / :n
end

show sim    1000 10000  ; 3.18
show sim   10000 10000  ; 3.1612
show sim  100000 10000  ; 3.145
show sim 1000000 10000  ; 3.140828