#region Header
#!/usr/bin/env python3
# from typing import *

import sys
import io
import math
import collections
import decimal
import itertools
from queue import PriorityQueue
import bisect
import heapq

def input():
    return sys.stdin.readline()[:-1]

sys.setrecursionlimit(1000000)
#endregion

# _INPUT = """# paste here...
# """
# sys.stdin = io.StringIO(_INPUT)


def main():
    N, M = map(int, input().split())
    s = []
    for _ in range(N):
        s.append(sum(list(map(int, input().split()))))

    dp = [[0, 0] for _ in range(N)]
    dp[0][0] = 0
    dp[0][1] = s[0]
    for i in range(1, N):
        dp[i][0] = max(dp[i-1][0], dp[i-1][1] - s[i])
        dp[i][1] = max(dp[i-1][1], dp[i-1][0] + s[i])

    v = max(dp[N-1])
    print(v)


if __name__ == '__main__':
    main()