mod = 1000000007
eps = 10**-9
inf = 10**20


def main():
    import sys
    input = sys.stdin.readline

    N, M = map(int, input().split())
    A = [0] * N
    for i in range(N):
        line = list(map(int, input().split()))
        A[i] = sum(line)

    dp = [[-inf] * 2 for _ in range(N+1)]
    dp[0][0] = 0
    for i in range(N):
        dp[i+1][1] = max(dp[i][1], dp[i][0] + A[i])
        dp[i+1][0] = max(dp[i][0], dp[i][1] - A[i])
    print(max(dp[-1]))


if __name__ == '__main__':
    main()