while (x = gets.to_i) != 0 
    score_ary = gets.split.map(&:to_i)
    a = 0
    m = score_ary.inject(:+) / score_ary.length.to_f
    for i in score_ary 
        a += (i - m)**2        
    end
    printf("%.4f\n", (a/score_ary.length)**0.5)
end
