It is a common etiquette for friends to shake hands when meeting each other. Five old friends shake hands once when they meet each other, how many times in total.
朋友间见面握手是一种常见的礼仪，5位老朋友见面相互握一次手，一共握了多少次．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">4 * (5/2)</gadget>
<output>10</output>

<result>10</result>