N, M = map(int, input().split())

matrix = [
    [*map(int, input().split())] for _ in range(N)
]

# M = 60
# N = 40
# matrix = [
#     [0]*M for _ in range(N)
# ]

matrix_sum = sum(sum(row) for row in matrix)

if N % 2 != 0 or M % 2 != 0:
    print(matrix_sum)
    exit(0)

minimum = 10**9

for i in range(N):
    for j in range(M):
        if i - j == 0 or i - j == N - M:
            # matrix[i][j] = '#'
            continue

        if (i == 0 and j == M - 2) or (i == 1 and j == M - 1) or (j == 0 and i == N - 2) or (j == 1 and i == N - 1):
            # matrix[i][j] = '?'
            continue

        minimum = min(minimum, matrix[i][j])

# print('\n'.join(map(str, matrix)))
#
# print(minimum)
print(matrix_sum - minimum)