#include <bits/stdc++.h>
using namespace std;

int main() {
  int N, M;
  cin >> N >> M;
  vector A(N + 1, 0L);
  for (int i = 0; i < N; i++) {
    for (long j = 0, a; j < M && cin >> a; j++) A.at(i) += a;
  }

  vector DP(N + 1, vector(2, LONG_MIN));
  DP.at(0).at(0) = 0;
  DP.at(0).at(1) = A.at(0);
  auto cmax = [&](long &a, long b) {if (a < b) a = b;};
  for (int i = 0; i < N; i++) {
    for (int j = 0; j < 2; j++) {
      long now = DP.at(i).at(j);
      if (j) {
        cmax(DP.at(i + 1).at(0), now - A.at(i + 1));
        cmax(DP.at(i + 1).at(1), now);
      } else {
        cmax(DP.at(i + 1).at(0), now);
        cmax(DP.at(i + 1).at(1), now + A.at(i + 1));
      }
    }
  }
  cout << max(DP.at(N - 1).at(0), DP.at(N - 1).at(1)) << "\n";
}