#!/usr/bin/env ruby

require 'trollop'


def usage
  STDERR.write "./avg [-r <d>] < <one number per line>\n"
  exit 1
end
usage if not [0,2].include? ARGV.size

opts = Trollop::options do
  opt :round, "Number of digits after decimal point.", :type => :int, :default => -1
end


sum = 0.0
i = 0
while line=STDIN.gets
  sum += line.strip.to_f
  i +=1
end

avg = sum/i.to_f

if opts[:round] >= 0
  puts avg.round opts[:round]
else
  puts avg
end