import
  algorithm, bitops, deques, heapqueue, math, macros, sets, sequtils,
  strformat, strutils, sugar, tables

proc input*(): string {.inline.} = stdin.readLine
proc inputs*(): seq[string] {.inline.} = stdin.readLine.split
proc inputInt*(): int {.inline.} = stdin.readLine.parseInt
proc inputInts*(): seq[int] {.inline.} = stdin.readLine.split.map(parseInt)
proc chmax*[T: SomeNumber](n: var T, m: T) {.inline.} = n = max(n, m)
proc chmin*[T: SomeNumber](n: var T, m: T) {.inline.} = n = min(n, m)
proc `%=`*[T: SomeInteger](n: var T, m: T) {.inline.} = n = floorMod(n, m)

when isMainModule:
  var N, M: int
  (N, M) = inputInts()
  var A = newSeqWith(N, inputInts())

  let B = collect(newSeq):
    for i in 0..<N: sum(A[i])
  
  const INF = 10^18
  var dp: array[1001, array[1001, int]]
  for i in 0..<N:
    dp[i].fill(-INF)
  dp[0][0] = 0
  for i in 0..<N:
    for j in 0..<N:
      dp[i + 1][j].chmax(dp[i][j])
      if j mod 2 == 0:
        dp[i + 1][j + 1].chmax(dp[i][j] + B[i])
      else:
        dp[i + 1][j + 1].chmax(dp[i][j] - B[i])
  echo max(dp[N])