The Coordinate Plane · Superchallenge problem

Grid points are numbered like this. $(0, 0)$ gets $1$. Then the points whose coordinates add to $1$ are numbered, starting from the $y$-axis: $(0, 1)$ gets $2$ and $(1, 0)$ gets $3$. Next come the points whose coordinates add to $2$: $(0, 2)$ gets $4$, $(1, 1)$ gets $5$, $(2, 0)$ gets $6$. This continues forever. What number does the point $(3, 5)$ get?