import sys
def main():
    input = sys.stdin.buffer.readline
    N, M = map(int, input().split())
    A = [sum(map(int, input().split())) for _ in range(N)]
    # dp_odd[n] := n 番目に奇数個食べたときの最大値
    dp_odd = [0] * (N+1)
    dp_even = [0] * (N+1)
    for i, a in enumerate(A, 1):
        dp_odd[i] = max(dp_even[:i]) + a
        dp_even[i] = max(dp_odd[:i]) - a
    print(max(dp_odd))

main()