n, m = map(int, input().split())
A = []
for _ in range(n):
    B = list(map(int, input().split()))
    A.append(sum(B))

INF = 10**18
DP = [[-INF for _ in range(2)] for _ in range(n + 1)]
DP[0][0] = 0
for i in range(n):
    DP[i + 1][1] = max(DP[i + 1][1], DP[i][1], DP[i][0] + A[i])
    DP[i + 1][0] = max(DP[i + 1][0], DP[i][0], DP[i][1] - A[i])
print(max(DP[n]))