Elementary school holds student calligraphy exhibition. Calligraphy works of students of each grade are displayed in the school window; 28 of them are not from the fifth grade, 24 are not from the sixth grade, and there are 20 calligraphy works from the fifth and sixth grades. The total number of works exhibited by grades 1 and 2 is 4 less than the total number of works exhibited by grades 3 and 4. How many calligraphy works are exhibited by grades 1 and 2?
小学举办学生书法展．学校的橱窗里展出每个年级学生的书法作品；其中有28幅不是五年级的，有24幅不是六年级的，五、六年级参展的书法作品共20幅．一、二年级参展的作品总数比三、四年级参展的作品的总数少4幅，一、二年级参展的书法作品共有多少幅．
<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">24 - 8</gadget>
<output>16</output>

<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<result>6</result>