#include<fstream>
#include<iostream>
using namespace std;
int main(){
	int n,m,a[100][100],s[100],suma=0,s1[100],d=-1,i,j;
	ifstream fi("flip.in");
	ofstream fo("flip.out");
	fi>>n>>m; 
	for( i=1;i<=n;i++)
	for( j=1;j<=m;j++){
	fi>>a[i][j];}
	for(i=1;i<=n;i++){
		s[i]=0;
		for(j=1;j<=m;j++){
			s[i]+=a[i][j];
			
			
			
			
		}
		if(s[i]<0){for(int k=1;k<=m;k++) a[i][k]=d*a[i][k];
		}
	}
	
	for(j=1;j<=m;j++){ s1[j]=0;for(i=1;i<=n;i++){ s1[j]+=a[i][j];
	}
	if(s1[j]<0) for(int k=1;k<=n;k++) a[k][j]=d*a[k][j];

	}
	
	
	
	for(i=1;i<=n;i++){
	
	for(j=1;j<=m;j++){
	
	suma+=a[i][j];} }
	fo<<suma;
	
	fi.close();
	fo.close();
	return 0;




}