There are 45 people in a certain class, 35 of them can play Chinese chess, 30 can play international chess, 38 can play Go, and 40 can play checkers. How many people in this class can know the above four kinds of chess?
某班共有45人，其中35人会中国象棋，30人会国际象棋，38人会围棋，40人会跳棋，可以肯定这个班至少有多少人以上四种棋都会？
<gadget id="calculator">45 - 35</gadget>
<output>10</output>

<gadget id="calculator">45 - 30</gadget>
<output>15</output>

<gadget id="calculator">45 - 38</gadget>
<output>7</output>

<gadget id="calculator">45 - 40</gadget>
<output>5</output>

<gadget id="calculator">10 + 15 + 7 + 5</gadget>
<output>37</output>

<gadget id="calculator">45 - 37</gadget>
<output>8</output>

<result>8</result>