Given a m x n matrix grid which is sorted in non-increasing order both row-wise and column-wise, return the number of negative numbers in grid.
Input: grid = [[4,3,2,-1],[3,2,1,-1],[1,1,-1,-2],[-1,-1,-2,-3]]
Output: 8
Explanation: There are 8 negatives number in the matrix.
Input: grid = [[3,2],[1,0]]
Output: 0
Input: grid = [[1,-1],[-1,-1]]
Output: 3
Input: grid = [[-1]]
Output: 1