Given an $m \times n$ matrix of distinct numbers, return the lucky number in the matrix.

A lucky number is an element of the matrix such that it is the smallest element in its row and largest in its column.

Constraints:

• $m =$ matrix.length

• $n =$ matrix[i].length

• $1 \leq n$, $m \leq 50$

• $1 \leq$ matrix[i][j] $\leq 10^5$

• All elements in the matrix are distinct.