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

using namespace std;

typedef long long ll;

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

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

	vector<vector<ll>> a(n, vector<ll>(m, 0));
	rep(i, n) rep(j, m) cin >> a[i][j];

	vector<ll> b(n, 0);
	rep(i, n) rep(j, m) b[i] += a[i][j];

	ll INF = 1e17;
	vector<vector<ll>> dp(n+1, vector<ll>(2, -INF));
	dp[0][0] = 0;
	rep(i, n){
		if(dp[i][0] != INF){
			chmax(dp[i+1][0], dp[i][0]);
			chmax(dp[i+1][1], dp[i][0] + b[i]);
		}

		if(dp[i][1] != INF){
			chmax(dp[i+1][0], dp[i][1] - b[i]);
			chmax(dp[i+1][1], dp[i][1]);
		}
	}

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