while true do
  n=STDIN.gets.split[0].to_i
  break if n==0
  ar=STDIN.gets.split
  sum=0
  0.upto(n-1){|i|
    sum += ar[i].to_f }
  mean = sum / n
  sum2=0
  0.upto(n-1){|i|
    sum2 += (ar[i].to_f-mean)*(ar[i].to_f-mean) }
  sd = Math::sqrt(sum2/n)
  puts "#{sd}"
end