There were 268 tadpoles in the water, and 139 of them turned into frogs. How many tadpoles are still in the water?
水中原有268只小蝌蚪，其中有139只变成了青蛙，还有多少只小蝌蚪在水中？
<gadget id="calculator">268 - 139</gadget>
<output>129</output>

<result>129</result>