Among the numbers 6, -1, 15, and -3, take any three different numbers and add them together. What is the smallest sum among them?
数6，-1，15，-3中，任取三个不同的数相加，其中和最小的是多少
<gadget id="calculator">(-1) + (-3) + 6</gadget>
<output>2</output>

<result>2</result>