def chmax(DP,i,v):
    if DP[i] < v: DP[i] = v
def chmin(DP,i,v):
    if DP[i] > v: DP[i] = v

N, M = map(int, input().split())
A = []
for i in range(N):
    a = list(map(int, input().split()))
    A.append(sum(a))

DP = [[-1] * (2) for _ in range(N + 1)]
# j == 0 ... 偶数個
# j == 1 ... 奇数個
DP[0][0] = 0

for i in range(N):
    for j in range(2):
        if DP[i][j] == -1:
            continue
        # 食べない
        chmax(DP[i + 1], j, DP[i][j])
        # 食べる
        dstj = j ^ 1
        chmax(DP[i + 1], dstj, DP[i][j] + A[i]*(dstj - j))

print(max(DP[-1]))