R,C = [int(x) for x in input().split()]

suma = 0
arr = []

for i in range(R):
    arr.append(list(map(int, input().split())))
    suma += sum(arr[-1])

arr[0][0] += 1000
arr[-1][-1] += 1000


if R%2 == 0 and C%2 == 0:
    minimum = 1000
    for line in arr:
        m = min(line)
        if m < minimum:
            minimum = m
    suma -= minimum
        

print(suma)