Exploding Dots

The $1 \leftarrow3$ machine:

• The dots initially go into the right most box.
• Whenever there are three (or more) dots are in the same box, then three dots will explode and become one dot on box to the left, unless there is no box one place to the left.

How many dots do we have to place to obtain the code $\boxed{1} \boxed{0}\boxed{2}\boxed{0}$ ?