while true do
	
	count = gets.to_i;
	
	if count == 0 then
		break;	
	end
	
	sum = 0.to_f;
	average = 0.to_f;
	
	aryStudentPoint = gets.split(' ').map(&:to_f);
	
	for sumIndex in 0..aryStudentPoint.length - 1 do
		
		sum = sum + aryStudentPoint[sumIndex];
		
	end
	
	average = sum / average;
	
	sum = 0.to_f;
	
	for index in 0..aryStudentPoint.length - 1 do
		
		sum = sum + (aryStudentPoint[index] - average) * (aryStudentPoint[index] - average)
		
	end
	
	puts "%.8f" % Math.sqrt(sum / count)
	
end