Xiaohong and some children stand in a row to play games. Xiaohong is the 10th person from the left and the 4th person from the right. How many children are playing games?
小红和一些小朋友站成一排做游戏，小红从左数是第10人，从右数是第4人，做游戏的小朋友一共有多少人．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">10 + 3</gadget>
<output>13</output>

<result>13</result>