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

int main() {
    int N, M;
    cin >> N >> M;
    ll A[N][M];
    ll b[N]{};
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++) {
            cin >> A[i][j];
            b[i] += A[i][j];
        }
    }
    ll d[N][2]{};
    d[0][0] = b[0];
    for (int i = 0; i < N - 1; i++) {
        d[i + 1][0] = max(d[i][1] + b[i + 1], d[i][0]);
        d[i + 1][1] = max(d[i][1], d[i][0] - b[i + 1]);
    }
    cout << max(d[N - 1][0], d[N - 1][1]) << "\n";
    return 0;
}