The line segment connecting any two points on the graph is called a chord. A circle can be divided into at most 4 pieces by a diameter and a chord. If it is divided by two diameters and a chord, it can be divided into 7 pieces at most. If you want to divide a circle into 31 pieces, at least how many diameters and a string are needed.
图上任意两点连接起来的线段叫做弦，一个圆被一条直径和一条弦所分最多可分4块，如果被两条直径和一条弦所分最多可分7块，如果要把一个圆分成31块，至少需要多少条直径与一条弦．
<gadget id="calculator">31 - 1</gadget>
<output>30</output>

<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<result>10</result>