There are 20 natural numbers, and their sum is 1999. Among these numbers, there are more odd numbers than even numbers. What is the maximum number of even numbers among these numbers?
有20个自然数，它们的和是1999，在这些数里，奇数的个数比偶数的个数多，这些数里偶数至多有多少个．
<gadget id="calculator">20 - 11</gadget>
<output>9</output>

<result>9</result>