def get$\_$down$\_$diagonal$\_$starts$($n: int$)->$ list$[$tuple$[$int$,$ int$]]$:

$"""$

Return a list of the valid down diagonal start coordinates in

an n$-$by$-$n grid.

The list must be ordered starting from the bottom$-$most starting coordinate

and ending with the right$-$most starting coordinate. See the examples below

and the diagrams in the supplemental materials for clarification.

Hint: this requires no helper to implement

Preconditions:

$-$ n $>=4$

$>>>$ get$\_$down$\_$diagonal$\_$starts$(4)$

$[(0,0)]$

$>>>$ get$\_$down$\_$diagonal$\_$starts$(5)$

$[(1,0),(0,0),(0,1)]$

$"""$ Please code in python