input: Write a python function to find the maximum sum of a cell and its adjacent top and left cells in a 2D matrix.
  assert find_max_sum([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == 18
  assert find_max_sum([[0, 0, 0], [0, 0, 0], [0, 0, 0]]) == 0
  assert find_max_sum([[1, 1, 1], [1, 1, 1], [1, 1, 1]]) == 3
output: def find_max_sum(matrix):
      max_sum = float('-inf')
      rows = len(matrix)
      cols = len(matrix[0])
      
      for i in range(1, rows):
          for j in range(1, cols):
              current_sum = matrix[i][j] + matrix[i-1][j] + matrix[i][j-1]
              max_sum = max(max_sum, current_sum)
      
      return max_sum