#include<iostream.h>
#include<fstream.h>
#include<math.h>
fstream f("flip.in", ios::in);
fstream g("flip.out",ios::out);
int main()
{
long long int n,m,v[100][16],i,j,poz=0,neg=0,poz1=0,neg1=0,s=0;
f>>n;
g<<" ";
f>>m;
for (i=1;i<=n;i++)
	   for (j=1;j<=m;j++)
		f>>v[i][j];
j=1;
while (j<=m)
	  {
	  for (i=1;i<=n;i++)
		       if (v[i][j]>=0) poz=poz+v[i][j];
				    else neg=neg+fabs(v[i][j]);
		       if (neg>poz) v[i][j]=v[i][j]*(-1);
j++;
}
i=1;
while (i<=n)
	    {
	    for (j=1;j<=m;j++)
			  if (v[i][j]>=0) poz1=poz1+v[i][j];
				    else neg1=neg1+fabs(v[i][j]);
		       if (neg1>poz1) v[i][j]=v[i][j]*(-1);
i++;
}
for (i=1;i<=n;i++)
	      for (j=1;j<=m;j++) s=s+v[i][j];
g>>s;
return 0;
}