Xiao Ming sent three kinds of letters at the post office, ordinary letters cost 8 cents each, airmail letters cost 1 cents each, and registered letters cost 2 cents each. She shared 1 yuan, 20 cents and 2 cents, so what is the minimum sum of his three kinds of letters? ．
小明在邮局寄了3种信，平信每封8分，航空信每封1角，挂号信每封2角，她共用了一元二角二分钱，那么他的三种信的总和最少是多少封．
<gadget id="calculator">4 + 4 + 1</gadget>
<output>9</output>

<result>9</result>