It takes 6901 numbers to number the pages of an encyclopedia for primary school students. How many pages does this book have?
一部小学生百科知识全书编上页码需要6901个数字，问这部书共有多少页？
<gadget id="calculator">90 * 2</gadget>
<output>180</output>

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

<gadget id="calculator">6_901 - 9 - 180 - 2_700</gadget>
<output>4_012</output>

<gadget id="calculator">4_012 / 4</gadget>
<output>1_003</output>

<gadget id="calculator">1_003 - 1</gadget>
<output>1_002</output>

<gadget id="calculator">1_000 + 1_002</gadget>
<output>2_002</output>

<result>2_002</result>