#include<iostream.h>
#include<fstream.h>
unsigned n,m;
long a[100][16];
ifstream f1("flip.in");
ofstream f2("flip.out");

void citire() {
	for(unsigned i=1;i<=n;i++)
		for(unsigned j=1;j<=m;j++)
			f1>>a[i][j];
}
void adun() {
	unsigned sn,sp,i,j,k;
	for( i;i<=n;i++){
		sn=0;sp=0;
		for( j=1;j<=m;j++) {

			if(a[i][j]>=0) sp+=a[i][j];
			else sn+=-a[i][j];
			if(sn>sp) for( k=1;k<=m;k++) a[i][k]=-a[i][k];
		}
	}
	for( i;i<=m;i++){
		sn=0;sp=0;
		for( j=1;j<=n;j++) {

			if(a[i][j]>=0) sp+=a[i][j];
			else sn+=-a[i][j];
			if(sn>sp) for( k=1;k<=n;k++) a[i][k]=-a[i][k];
		}
	}
}
int main() {
	f1>>n>>m;
	long s=0;
	if(n>=1 && m<=16) {
		citire();
		adun();
	
		for(unsigned i=1;i<=n;i++)
			for(unsigned j=1;j<=m;j++)
				s+=a[i][j];
		f2<<s;
	}
	f1.close();
	f2.close();

	return 0;
}