class of natural numbers, starting from the third number, each number is exactly the sum of the previous two numbers, such as 123, 235, etc. How many such three-digit numbers are there?
一类自然数，从第三个数字开始，每个数字都恰好是它前面两个数字的和，如123，235等等，这类三位数共有多少个．
<gadget id="calculator">1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9</gadget>
<output>45</output>

<result>45</result>