while true
        n = STDIN.gets.to_i
        if n == 0 then
                puts 0.0
                break
        end
        s = STDIN.gets.split(' ')
        s.each_with_index {|v,i| s[i] = v.to_i }
        m = s.inject(:+) / n
        alpha = 0.0
        s.each {|v|
                alpha += (v - m) * (v - m)
        }
        alpha /= n
        puts Math.sqrt(alpha)
end