If you read 50 pages of a book every day, then you can’t finish it in 5 days, but you have more than 6 days; if you read 70 pages a day, you can’t finish it in 3 days, but you have more than 4 days; if you read n pages a day, you can use just n days Finish reading (n is a natural number). What is the number of pages in this book.
一本书，如果每天读50页，那么5天读不完，6天又有余；如果每天读70页，那么3天读不完，4天又有余；如果每天读n页，恰可用n天读完(n是自然数)．这本书的页数是多少．
<gadget id="calculator">16 * 16</gadget>
<output>256</output>

<result>256</result>