A glass of water is 2 liters, x ml is poured out each time, how many ml is left after pouring 4 times.
一杯水2升，每次倒出x毫升，倒了4次后还剩下多少毫升．
<gadget id="calculator">2 * 1_000</gadget>
<output>2_000</output>

<gadget id="calculator">2_000 - 4</gadget>
<output>1_996</output>

<result>1_996</result>