For positive integers a and b, a△b is equal to the sum of b consecutive positive integers starting from a, such as: 2△3=2+3+4, and another example: 5△4=5+6+7+8= 26． If y△3=12, then y=how much.
对正整数a、b，a△b等于由a开始的连续b个正整数之和，如：2△3=2+3+4，又如：5△4=5+6+7+8=26．若y△3=12，则y=多少．
<result>3</result>