Most of the keys of a calculator are disabled, only the numbers "7" and "0" and the addition key "+" can still be used, so it is possible to input 77, 707, which contains the numbers 7 and 0 and numbers, and can only be used for addition Operation, in order to display 864192, how many times should you press the "7" key at least.
一台计算器大部分按键失灵，只有数字"7"和"0"，以及加法键"+"尚能使用，因此可能输入77、707这样办含数字7和0和数，并用只能进行加法运算，为了显示出864192，那么最少要按"7"键多少次．
<gadget id="calculator">6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>21</output>

<result>21</result>