For any dataset $X = \{x_1, x_2, \dots, x_n\}$ of size $n \geq 2$ with an unbiased sample standard deviation $s > 0$ and a mean absolute deviation from the mean $\text{MAD} = \frac{1}{n} \sum_{i=1}^n |x_i - \bar{x}|$, which of the following inequalities represents the sharpest upper bound for the ratio $\frac{\text{MAD}}{s}$?