while n = gets
    student = n.chomp.to_i
    break if student == 0
    
    s = gets.split.map(&:to_i)
    m = s.inject(:+) / s.length
    sum = s.inject(0){|sum, i| sum + (i - m) ** 2 }
    puts alpha = (sum / student) ** (1 / 2.0)
end

