Xiao Li travels from city A to city B at a speed of 5 km/h. Xiaolan travels from city B to city A at a speed of 4 km/h. The two started at the same time, and they met at a place 1 km away from the midpoint of the two cities A and B. Find the distance between the two cities A and B?
小李从A城到B城，速度是5千米/时．小兰从B城到A城，速度是4千米/时．两人同时出发，结果在离A、B两城中点1千米的地方相遇，求A、B两城间的距离？
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">5 - 4</gadget>
<output>1</output>

<gadget id="calculator">2 / 1</gadget>
<output>2</output>

<gadget id="calculator">1 * 2</gadget>
<output>2</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>