For the numbers a, b, c, d stipulate <a, b, c, d>=2ab-c+d. If <1, 3, 5, x>=7, then x=how much.
对于数a，b，c，d规定＜a，b，c，d＞=2ab-c+d．如果＜1，3，5，x＞=7，那么x=多少．
<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">7 - 6</gadget>
<output>1</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<result>6</result>