#include<fstream>
using namespace std;
int a[20][20],n,m,s1,s2,smax;
ifstream f("flip.in");
ofstream g("flip.out");
void suma();
int main()
{
    int i,j;
    f>>n>>m;
    for(i=1;i<=n;i++)
    for(j=1;j<=m;j++)
        f>>a[i][j];
   suma();
    return 0;
}

void suma()
{
    s1=s2=0;
    int i,j;
    for(i=1;i<=n;i++)
    for(j=1;j<=m;j++)
        if(a[i][j]>=0)
        s1+=a[i][j];
        else
        s2-=a[i][j];
    if(s2>s1)
    g<<s2;
    else
    g<<s1;
}