How well you know greatest integer function?

Let $f(x)$ be a continuous function whose range is $[2,6.5]$ .

If $h(x)=\left\lfloor \dfrac { \cos x+f(x) }{ \lambda } \right\rfloor ,\lambda \in \mathbb N$ be continuous, where $\left\lfloor . \right\rfloor$ denotes the greatest integer function, then the least value of $\lambda$ is: