A batch of optical discs sold 25% of the total number on the first day, 450 copies on the second day, one-third of the sum of the sales in the first two days on the third day, and finally 200 copies. Find the original number of optical discs how many?
一批光碟，第一天卖出总数的25%，第二天卖出450张，第三天卖出的是前两天卖出的总和的三分一，最后剩下200张，求光碟的总数原有多少？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">450 * (1/3)</gadget>
<output>150</output>

<gadget id="calculator">450 + 150 + 200</gadget>
<output>800</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) * (1/3)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 - (1/4) - (1/12)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">800 / (2/3)</gadget>
<output>1_200</output>

<result>1_200</result>