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

const ll mod = 1000000007;
const int INF = 1001001001;

ll dp[2][1001];

int main(){
    int n, m; cin >> n >> m;
    vector<ll> happy(n);
    for(int i = 0; i < n; i++){
        ll sum = 0;
        for(int j = 0; j < m; j++){
            ll k; cin >> k;
            sum += k;
        }
        happy[i] = sum;
    }
    for(int j = 0; j < 2; j++){
        for(int k = 0; k < 1001; k++){
            dp[j][k] = -INF;
        }
    }
    dp[0][0] = 0;
    for(int i = 1; i <= n; i++){
        for(int j = 0; j < 2; j++){
            dp[j][i] = max(dp[j][i], dp[j][i - 1]);
        }
        for(int j = 0; j < 2; j++){
            dp[j][i] = max(dp[j][i], dp[(j + 1) % 2][i - 1] + (j == 0 ? -1 : 1) * happy[i - 1]);
        }
    }
    cout << max(dp[0][n], dp[1][n]) << endl;
}