$stdin = DATA if $stdin.eof?

ARGF.each do |line|
  break if line =~ /0/
  points = gets.split.map(&:to_i)

  avg = points.inject(:+) / points.size

  ? = points.inject(0){|ret, p| ret + (p - avg)**2 / points.size }
  puts Math.sqrt(?)
end

__END__
5
70 80 100 90 20
3
80 80 80
0