Only "7","0","+"allowed

Logic Level 3

A malfunction calculator can only perform calculation using $$"7", "0"$$ and $$"+"$$ keys. That means number such as $$"77707"$$ could still be keyed-in for the addition operation. What is the least number of times that the $$"7"$$ key must be used in the addition process to view $$"222222"$$ on its screen?

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