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 / count;
	
	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