while input = gets

    n = input.to_f
    
    if n == 0
        exit
    end
    
    scores = gets.chomp.split(" ").map(&:to_i)
    
    sum1 = 0
    sum2 = 0
    scores.each do |x|
        sum1 += x
        sum2 += (x ** 2)
    end
    
    sx = ((sum2 / n) - (sum1 / n) ** 2.0) ** (1/2.0)
    
    puts sprintf("%.8f", sx)
end
