#include<fstream>
using namespace std;
long int s=0,k=0,v[100][100],m,n,i,j;
int main ()
{
ifstream in("flip.in");
ofstream out("flip.out");
in>>n;
in>>m;
for (i=1;i<=n;i++)
  for (j=1;j<=m;j++)
 { in>>v[i][j];
  if (v[i][j]>0) s=s+v[i][j];
  if (v[i][j]<0) k=k+v[i][j];}
k=k*(-1);
if (s>k) out<<s;
else out<<k;
out<<s;
in.close();
out.close();
return 0;
}