#include <iostream>
#include <algorithm>
#define int long long
#define rep(i, n) for(i = 0; i < n; i++)
using namespace std;

void chmax(int &a, int b) { a = max(a, b); }

int n, m;
int a[1000];
int dp[1001][2];

signed main() {
	int i, j;
	
	cin >> n >> m;
	rep(i, n) {
		rep(j, m) {
			int x;
			scanf("%lld", &x);
			a[i] += x;
		}
	}
	
	int INF = 1e+16;
	rep(i, n + 1) rep(j, 2) dp[i][j] = -INF;
	
	dp[0][0] = 0;
	rep(i, n) {
		rep(j, 2) {
			chmax(dp[i + 1][j], dp[i][j]);
			chmax(dp[i + 1][!j], dp[i][j] + a[i] * (j == 0 ? 1 : -1));
		}
	}
	
	cout << max(dp[n][0], dp[n][1]) << endl;
	return 0;
}