Differential Equations · Medium problem

For $\dfrac{dy}{dx}=y$, $y(0)=1$, Euler's method is used with $n$ equal steps over $[0,1]$, and the error compared to the exact value $y(1)=e$ is measured. Since Euler's method is a first-order method, its error is roughly proportional to the step size. If the number of steps is doubled, by about what factor does the error decrease?