#include <fstream>
using namespace std;
ifstream f("flip.in");
ofstream g("flip.out");
int main()
{
    int m,n,S1=0,S2=0,i,j,x;
    f>>n>>m;
    for(i=1;i<=n;++i)
    {
        for(j=1;j<=m;++j)
        {
             f>>x;
             if(x>0)
                S1+=x;
             else
                S2+=x;
        }
    }
    if(S1>S2)
        g<<S1;
    else
        g<<S2;
}