import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**16
md = 998244353
# md = 10**9+7

n, m = LI()
aa = LLI(n)
ss = []
for row in aa:
    ss.append(sum(row))

def chmax(i, j, val):
    if val > dp[i][j]: dp[i][j] = val

dp = [[-inf]*2 for _ in range(n+1)]
dp[0][1] = 0
for i in range(n):
    for j in range(2):
        pre = dp[i][j]
        if pre==-inf:continue
        if j:
            chmax(i+1, 0, pre+ss[i])
            chmax(i+1, 1, pre)
        else:
            chmax(i+1, 1, pre-ss[i])
            chmax(i+1, 0, pre)

print(max(dp[-1]))