#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (int)(n); ++i)
using namespace std;
using ll = long long;

template<class T> inline bool chmin(T& a, T b) {
    if(a > b) {
        a = b;
        return true;
    }
    return false;
}

template<class T> inline bool chmax(T& a, T b) {
    if(a < b) {
        a = b;
        return true;
    }
    return false;
}
struct Unionfind {
    vector<int> par;

    Unionfind(int n) : par(n) {
        for(int i = 0; i < n; ++i) par[i] = i;
    }

    int root(int x) {
        if(par[x] == x) return x;
        return par[x] = root(par[x]);
    }

    void unite(int x, int y) {
        int rx = root(x);
        int ry = root(y);
        if(rx == ry) return;
        par[rx] =ry;
    }

    bool same(int x, int y) {
        int rx = root(x);
        int ry = root(y);
        return rx == ry;
    }
};

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    int n, m;
    cin >> n >> m;

    vector<ll> a(n);
    rep(i, n) {
        ll t = 0;
        rep(j, m) {
            int ac;
            cin >> ac;
            t += ac;
        }
        a[i] = t;
    }

    vector<vector<ll>> dp(n, vector<ll>(2));
    dp[0][0] = a[0];
    dp[0][1] = 0;

    for(int i = 0; i < n - 1; ++i) {
        dp[i+1][0] = max(dp[i][1] + a[i+1], dp[i][0]);
        dp[i+1][1] = max(dp[i][0] - a[i+1], dp[i][1]);
    }

    cout << max(dp[n-1][0], dp[n-1][1]) << endl;
    return 0;
}