If \( f:\mathbb{R}\to\mathbb{R} \) is given by \( f(x)=x+1 \), then the value of \( \displaystyle \lim_{n \to \infty} \dfrac{1}{4} \left[ f(0) + f\left(\dfrac{5}{n}\right) + f\left(\dfrac{10}{n}\right) + ... + f\left(\dfrac{5(n - 1)}{n}\right) \right],\) is:
