amazon | Maximum Sum of an Hourglass

class Solution:
    def maxSum(self, grid: List[List[int]]) -> int:
        maxi=-1e20
        n=len(grid)
        m=len(grid[0])
        for i in range(n-2):
            for j in range(m-2):
                sumi=grid[i][j]+grid[i+1][j+1]+grid[i+2][j+2]+grid[i][j+1]+grid[i][j+2]+grid[i+2][j]+grid[i+2][j+1]
                maxi=max(maxi,sumi)
        return maxi