There are 99 students in the sixth grade of Yucai Primary School, and every 3 students are divided into a group to play games. Among the 33 groups, there are 5 groups with only 1 boy, and 18 groups with 2 or 3 girls. There are as many groups with 3 boys as with 3 girls. How many boys are there in the sixth grade? ．
育才小学六年级共有学生99人，每3人分成一个小组做游戏．在这33个小组中，只有1名男生的共5个小组，有2名或3名女生的共18个小组，有3名男生和有3名女生的小组同样多，六年级共有男生多少名．
<gadget id="calculator">18 - 5</gadget>
<output>13</output>

<gadget id="calculator">33 - 13 - 13 - 5</gadget>
<output>2</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">99 / 33</gadget>
<output>3</output>

<gadget id="calculator">13 * 3</gadget>
<output>39</output>

<gadget id="calculator">1 * 5</gadget>
<output>5</output>

<gadget id="calculator">4 + 39 + 5</gadget>
<output>48</output>

<result>48</result>