Major and Minor Axes, Vertices and Co-Vertices of an Ellipse

Let $N$ be the number of ordered pairs of integers $(x, y)$ such that $$4x^2 + 9y^2 \le 1000000000.$$ Let $a$ be the first digit of $N$ (from the left) and let $b$ be the second digit of $N$. What is the value of $10a + b$?

Source: Math Prize for Girls