#include<bits/stdc++.h>
using namespace std;
#define ll long long 
int m,n;
ll x[20001],tot;
int main()
{
    freopen("perfecttour.in","r",stdin);
    freopen("perfecttour.out","w",stdout);
    cin>>n>>m;
    for(int i=1;i<m;++i)
    x[i]=-INT_MAX;
    for(int i=1;i<=n;++i)
    {
        for(int j=1;j<m;++j)
        {
            ll a;
            cin>>a;
            x[j]=max(x[j],a);
        }
    }
    for(int i=1;i<m;++i)
    tot+=x[i];
    ll ans=0;
    int ls=1;
    for(int l=1;l<m;++l)
    {
       ans+=x[l];
       if(ans<0)
       {
            tot-=ans;
            ans=0;    
            ls=l;
       }        
    }
    ans=0;
    for(int r=m-1;r>ls;--r)
    {
       ans+=x[r];
       if(ans<0)
       {
            tot-=ans;
            ans=0;    
       }     
    }
    cout<<tot;
    return 0;
}