The students in Class 1 of the fourth grade have subscribed three kinds of periodicals A, B and C, and each of them has subscribed to 2 different periodicals, including 28 periodicals of type A, 36 periodicals of type B and 38 periodicals of type C. Then, how many students are there who subscribe to both type A periodical and type C periodical?
四年级1班的学生订阅了甲、乙、丙三种期刊，且每人都订阅了2种不同的期刊，其中甲种期刊28本，乙种期刊36本，丙种期刊38本．那么，既订阅甲种期刊又订阅丙种期刊的学生有多少人．
<gadget id="calculator">28 + 38</gadget>
<output>66</output>

<gadget id="calculator">28 + 36 + 38</gadget>
<output>102</output>

<gadget id="calculator">102 / 2</gadget>
<output>51</output>

<gadget id="calculator">66 - 51</gadget>
<output>15</output>

<result>15</result>