Numerical Methods: Euler to Runge–Kutta · Medium problem

A biologist models early bacterial growth by $y' = y$ (population, in millions), $y(0) = 1$. The local truncation error of one Euler step is approximated by $\dfrac{h^2}{2}y''(t_0)$; for this equation $y'' = y' = y$, so at $t_0 = 0$ it equals $\dfrac{h^2}{2}$. What is the largest step size $h > 0$ that keeps this estimated first-step error at or below $0.005$? Express your answer as a decimal, to at least two places.