#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("YES");}else{puts("NO");}
#define MAX_N 200005

int main() { 
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int n, m;
    cin >> n >> m;
    ll a[n] = {};
    rep(i,n){
        rep(j,m){
            ll x;
            cin >> x;
            a[i] += x;
        }
    }
    ll dp[n][2];
    dp[0][0] = 0;
    dp[0][1] = a[0];
    srep(i,1,n){
        dp[i][0] = max(dp[i-1][0], dp[i-1][1]-a[i]);
        dp[i][1] = max(dp[i-1][1], dp[i-1][0]+a[i]);
    }
    cout << max(dp[n-1][0],dp[n-1][1]) << endl;
    return 0;
}