#!/usr/local/bin/ruby
# Compute mean process turn-around time for list of run lengths.

if ARGV.empty?
    $stderr.puts "Usage #{File::basename($0)} <time1> [[<time2>] ...]"
    exit 64
end
n = t = tt = 0
ARGV.each do |a|
    n+= 1
    t+= a.to_i
    tt+= t
end
puts (tt / n)