A warehouse robot is placed in an m x n storage grid. The robot starts at the top-left storage position, grid[0][0], and must reach the bottom-right storage position, grid[m - 1][n - 1].

At any point, the robot can only move either down to the next aisle or right along the aisle.

Given the two integers m and n, return the number of possible unique paths the robot can take to reach the final storage position.

Example 1:

Input: m = 3, n = 6
Output: 21
Explanation: The storage grid has 3 rows and 6 columns.
The robot starts at the top-left position and must reach bottom-right position.
Since the robot can only move right or down, every valid path must contain:
2 down moves, 5 right moves
There are 21 unique ways to arrange these moves, so the output is 21.

Example 2:

Input: m = 2 , n = 3
Output: 3
Explanation: The robot starts at grid[0][0] and must reach grid[1][2].
Right → Right → Down
Right → Down → Right
Down → Right → Right

Example 3:

Input: m = 1 , n = 5
Output: 1 
Explanation: There is only one row in the grid, So, there is only one possible path: Right → Right → Right → Right

Constraints

1 <= m <= 100

1 <= n <= 100
The answer will be less than or equal to

51. Robot Unique Paths