A certain person goes to the street to do business, and only buys 1 catty of fish each time. If he bought it at 3 yuan a catty and sold it at 4 yuan a catty; and then bought it at 5 yuan a catty and sold it at 6 yuan a catty. How much did he earn?
某人上街做买卖，每次只买1斤鱼．如果他以3元一斤买进，4元一斤卖出；然后又以5元一斤买进，6元一斤卖出．他赚了多少元钱．
<gadget id="calculator">4 - 3</gadget>
<output>1</output>

<gadget id="calculator">6 - 5</gadget>
<output>1</output>

<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<result>2</result>