Arrange 8 numbers in a row, and each subsequent number is exactly equal to the sum of the two preceding numbers. If the seventh and eighth numbers are 73 and 118 respectively, what is the first number?
将8个数排成一列，每后一个数都恰好等于它前面两个数之和，如果第七个数和第八个数分别是73和118，那么第一个数是多少．
<gadget id="calculator">118 - 73</gadget>
<output>45</output>

<gadget id="calculator">73 - 45</gadget>
<output>28</output>

<gadget id="calculator">45 - 28</gadget>
<output>17</output>

<gadget id="calculator">28 - 17</gadget>
<output>11</output>

<gadget id="calculator">17 - 11</gadget>
<output>6</output>

<gadget id="calculator">11 - 6</gadget>
<output>5</output>

<result>5</result>