Differential Equations

Suppose \(y=y(x)\) be the solution curve to the differential equation \(\frac{d y}{d x}-y=2-e^{-x}\) such that \(\lim\limits_{x \rightarrow \infty} y(x)\) is finite. If \(a\) and \(b\) are respectively the \(x\) - and \(y\)-intercepts of the tangent to the curve at \(x=0\), then the value of \(a-4 b\) is equal to _____________.