#include<fstream.h>
int main ()
{
	ifstream fcin("flip.in");
	ofstream fcout("flip.out");
	long int N,M,x[300],i,j,s=0;
	fcin>>N>>M;
	x[0]=0;
	for(i=1;i<=N*M;i++)fcin>>x[i];
	for(j=1;j<=N;j++){s=0;
						for(i=(j-1)*M+1;i<=M*j;i++)s=s+x[i];
						if(s<0){for(i=(j-1)*M+1;i<=M*j;i++){x[i]=x[i]*-1;}}}
	for(i=0;i<=M-1;i++){s=0;
						for(j=i+1;j<=N*M;j=j+M){s=s+x[j];}
						if(s<0){for(j=1+i;j<=N*M;j=j+M){x[j]=x[j]*-1;}}}
	s=0;
	for(i=1;i<=N*M;i++)s=s+x[i];
	fcout<<s;
	return 0;
}