$stdin = DATA if $stdin.eof?

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

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

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

__END__
5
70 80 100 90 20
3
80 80 80
1
100
1
50
1
0
10
0 0 0 0 0 0 0 0 0 0
10
1 34 44 63 30 1 9 53 57 57
10
20 12 52 44 6 9 94 31 67 70
0