The school reissues student ID cards to all students in the school. Each student ID card has a number, and the number of 2200 students starts from 1 to 2200. Q: How many digits are there in the student ID number?
学校给全校学生换发学生证．每个学生证都有编号，2200名学生编号从1号起至2200号．问：学生证编号码共有多少数字？
<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<gadget id="calculator">9 * 1</gadget>
<output>9</output>

<gadget id="calculator">99 - 10</gadget>
<output>89</output>

<gadget id="calculator">89 + 1</gadget>
<output>90</output>

<gadget id="calculator">90 * 2</gadget>
<output>180</output>

<gadget id="calculator">999 - 100</gadget>
<output>899</output>

<gadget id="calculator">899 + 1</gadget>
<output>900</output>

<gadget id="calculator">900 * 3</gadget>
<output>2_700</output>

<gadget id="calculator">2_200 - 1_000</gadget>
<output>1_200</output>

<gadget id="calculator">1_200 + 1</gadget>
<output>1_201</output>

<gadget id="calculator">1_201 * 4</gadget>
<output>4_804</output>

<gadget id="calculator">9 + 180 + 2_700 + 4_804</gadget>
<output>7_693</output>

<result>7_693</result>