#include<fstream.h>
int main ()
{
	ifstream fcin("flip.in");
	ofstream fcout("flip.out");
	long int N,M,x[257],i,j,s=0;
	fcin>>N>>M;
	for(i=1;i<=N*M;i++)fcin>>x[i];
	for(j=1;j<=N;j++){s=0;
						for(i=(j-1)*M;i<=M*j;i++)s=s+x[i];
						if(s<0){for(i=(j-1)*M;i<=M*j;i++)x[i]=-1*x[i];}}
	for(i=0;i<=M-1;i++){s=0;
						for(j=1+i;j<=N+i;j=j+M)s=s+x[j];
						if(s<0){for(j=1+i;j<=N+i;j=j+M)x[j]=-1*x[j];}}
	s=0;
	for(i=1;i<=N*M;i++)s=s+x[i];
	fcout<<s;
	return 0;
}