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

mat = []
for i in range(N):
    mat.append(list(map(int, input().split())))

summa = 0
if N % 2 == 1 or M % 2 == 1:
    for i in mat:
        summa += sum(i)
    print(summa)
elif (N % 2 == 0 and M == 1) or (M % 2 == 0 and N == 1):
    for i in mat:
        summa += sum(i)
    print(summa)
else:
    for i in mat:
        summa += sum(i)
    summa1 = summa - mat[N - 2][M - 1]
    summa2 = summa - mat[N - 1][M - 2]
    print(max(summa1, summa2))