while true
        n = STDIN.gets.chomp.to_i
        break if n == 0
        s = STDIN.gets.split(' ').collect {|v| v.to_f}
        m = s.inject(:+) / n
        alpha = 0.0
        s.each {|v|
                alpha += (v - m) ** 2
        }
        puts Math.sqrt(alpha / n)
end