Five Doors, One Switch

In a game show there are $5$ doors: a car is behind one, goats behind the other four. You pick a door. The host, who knows what's behind each door, then opens $3$ of the remaining $4$ doors, all revealing goats, leaving your original pick and one other door closed. If you switch to that remaining door, what is your probability of winning the car? The answer is in the form $\frac{\alpha}{\beta}$ for coprime integers $\alpha$ and $\beta$. Input the answer as the sum $\alpha +\beta$.