while true
    num = gets.to_i
    if num == 0
        break
    else
        numbers = gets.split.map(&:to_f)
        abverage = numbers.reduce(:+)/numbers.length
        stdv = 0
        numbers.each do |num|
            stdv += (num-abverage)**2
        end
        puts "#{sprintf("%.4f",(stdv/numbers.length)**0.5)}"
    end
end
