total of 138 students in four grades of a certain school participated in the mathematics competition, including 70 students in the first and second grades, 65 students in the first and third grades, 59 students in the second and third grades, and how many students in the fourth grade?
某校四个年级共138名学生参加数学竞赛，其中一、二年级共70名，一、三年级共65名，二、三年级共59名，四年级有多少名？
<gadget id="calculator">70 + 65 + 59</gadget>
<output>194</output>

<gadget id="calculator">194 / 2</gadget>
<output>97</output>

<gadget id="calculator">138 - 97</gadget>
<output>41</output>

<result>41</result>