from itertools import accumulate
n, m = map(int, input().split())
a = [sum(list(map(int, input().split()))) for i in range(n)]
cnt = 0
cnt2 = 0
l = [0]
l2 = [0]
for i in range(n):
    if i % 2 == 0:
        cnt += a[i]
        cnt2 -= a[i]
    else:
        cnt -= a[i]
        cnt2 += a[i]
    l.append(cnt)
    l2.append(cnt2)
ans = 0
for i in range(n):
    for j in range(i, n):
        ans = max(ans, l[j + 1] - l[i], l2[j + 1] - l2[i])
print(ans)