A and B start climbing from the foot of the mountain at the same time, and descend immediately after reaching the top of the mountain. The speed of A and B going down the mountain is twice the speed of their respective uphill. When A reaches the top of the mountain, B is still 500 meters away from the top of the mountain. A returns to the foot of the mountain. Shi B just descended halfway up the mountain, and asked for the distance from the foot of the mountain to the top of the mountain.
甲，乙两人同时从山脚开始爬山，到达山顶后立即下山，甲，乙两人下山的速度都是各自上山速度的2倍，甲到山顶时乙距山顶还有500米，甲回到山脚时乙刚好下到半山腰，求山脚到山顶的距离．
<gadget id="calculator">2 * 500</gadget>
<output>1_000</output>

<gadget id="calculator">500 + 1_000</gadget>
<output>1_500</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 * (1/2) * (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1_500 / (1/2)</gadget>
<output>3_000</output>

<result>3_000</result>