def pr(f)
  printf "%f\n",f
end
def calc(ar)
  ave = ar.sum/ar.size.to_f
  var = ar.inject(0.0) do |sum,f|
    sum + (f-ave)**2
  end
  var = var/ar.size
  return Math.sqrt(var)
end
def code_run
  until (iN=$stdin.gets.to_i)==0 do
    pr calc($stdin.gets.split.map(&:to_i))
  end
end

code_run
