dims = input().split(" ")
rows = int(dims[0])
cols = int(dims[1])

rowData = []
for i in range(rows):
    l = input().split(" ");
    for i in range(l.__len__()):
        l[i] = int(l[i])
    rowData.append(l)


sum = 0
for row in rowData:
    for item in row:
        sum += item

# alespon 1 lichy rozmer
if (rows % 2 == 1) or (cols % 2 == 1):
    print(sum)
    exit(0)

# obe souradnice sude
maxSum = 0
for r in range(rows):
    for c in range(cols):
        if r == c: # diagonal
            continue
        if (r == 0) and (c == cols - 2): # corners
            continue
        if (r == 1) and (c == cols - 1):
            continue
        if (r == rows - 2) and (c == 0):
            continue
        if (r == rows - 1) and (c == 1):
            continue

        maxSum = max(maxSum, sum - rowData[r][c])

print(maxSum)