from itertools import accumulate
n, m = map(int, input().split())
a = [sum(list(map(int, input().split()))) for i in range(n)]
dp = [[0] * n for i in range(n)]
dp[0][0] = a[0]
for i in range(n):
    for j in range(n):
        if not (i == 0 and j == 0):
            dp[i][j] = max(dp[i - 1][j], dp[i][j - 1] + a[j]) if j % 2 else max(dp[i - 1][j], dp[i][j - 1] - a[j])
print(max(dp[-1]))