
loop do
    n = gets.to_i
    
    if n == 0 then
        break
    end
    
    a = gets.split(" ").map(&:to_f)
    
    b = a.sum / a.size
    
    k = 0
    a.each do |i|
        k += (i - b) * (i - b)
    end
    
    print Math.sqrt(k / a.size), "\n"
end
