Students in three classes of the third grade planted a tree every 2 meters on one side of a 180-meter-long embankment, planting both ends. It is known that counting from left to right, the 56th tree to the right is planted by the second class; counting from the right to the left, the 60th tree is planted by the third class to the left; then, the third grade is planted by the first class how many trees
三年级三个班的学生在一条长180米的河堤的一边每隔2米种一棵树，首尾都种．已知从左往右数，第56棵树起往右都是二班种的；从右往左数，第60棵树起往左都是三班种的；那么，三年级一班种了多少棵树？
<gadget id="calculator">180 / 2</gadget>
<output>90</output>

<gadget id="calculator">90 + 1</gadget>
<output>91</output>

<gadget id="calculator">91 - 56</gadget>
<output>35</output>

<gadget id="calculator">35 + 1</gadget>
<output>36</output>

<gadget id="calculator">91 - 60</gadget>
<output>31</output>

<gadget id="calculator">31 + 1</gadget>
<output>32</output>

<gadget id="calculator">91 - 36 - 32</gadget>
<output>23</output>

<result>23</result>