good friends shake hands once when they meet each other, how many times should they shake hands in total?
4个好朋友见面互相握手一次，共要握手多少次次．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<result>6</result>