The most ideal and perfect number in the eyes of the ancient Greeks is just the sum of all the factors of this number (except itself). For example: 6 has four factors 1, 2, 3, 6, except 6, there are three factors of 1, 2, 3. 6=1+2+3 is exactly the sum of all factors, so 6 is the most ideal and perfect number. Such numbers are called "perfect numbers". How much of the following is a "perfect number".
古希腊人心目中最理想、最完美的数恰好由这个数的所有因数(本身除外)相加之和．例如：6有四个因数1、2、3、6，除去6之外，还有1、2、3三个因数．6=1+2+3，恰好是所有因数之和，所以6是最理想、最完美的数．这样的数被叫做"完全数"．下面多少是"完全数"．
<gadget id="calculator">1 + 2 + 4 + 7 + 14</gadget>
<output>28</output>

<result>28</result>