#include<bits/stdc++.h>

using namespace std;
using ll=long long;
#define rep2(i, a, n) for(int i = (a); i < (n); i++)
#define rep(i, n) rep2(i,0,n)
template<class T>
inline bool chmax(T& a, T b){if(a<b){a=b;return true;} return false;}

int main(){
  cin.tie(nullptr);ios_base::sync_with_stdio(false);
  int n,m;cin>>n>>m;
  ll hoge;
  vector<ll> a(n,0);
  rep(i,n){
    rep(j,m){
      cin>>hoge;
      a[i]+=hoge;
    }
  }

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

  rep(i,n-1){
    dp[i+1][0]=max(dp[i][0],dp[i][1]+a[i+1]);
    dp[i+1][1]=max(dp[i][1],dp[i][0]-a[i+1]);
  }
  /*
  rep(i,n){
    cout<<a[i]<<" ";
  }
  cout<<endl;
  cout<<endl;
  rep(i,n){
    cout<<dp[i][0]<<" "<<dp[i][1]<<endl;
  }
  */
  cout<<max(dp[n-1][0],dp[n-1][0])<<endl;
}