#include<stdio.h>

long a[19][19],s,sf;
int i,j,n,m;

int main()
{
	freopen("flip.in","r",stdin);
	freopen("flip.out","w",stdout);

	scanf("%d%d",&n,&m);
	for(i=1;i<=n;++i)
	{
		s=0;
		for(j=1;j<=m;++j)
		{
			scanf("%ld",&a[i][j]);
			s+=a[i][j];
		}
		if(s<0)
			for(j=1;j<=m;++j)
				a[i][j]*=-1;
	}
	int c=1;
	while(c)
	{
		c=0;
		for(i=1;i<=m;++i)
		{
			s=0;
			for(j=1;j<=n;++j)
				s+=a[j][i];
			if(s<0)
			{
				for(j=1;j<=n;++j)
					a[j][i]*=-1;
				c=1;
			}
		}
		for(i=1;i<=n;++i)
		{
			s=0;
			for(j=1;j<=m;++j)
				s+=a[i][j];
			if(s<0)
			{
				for(j=1;j<=m;++j)
					a[i][j]*=-1;
				c=1;
			}
		}
	}
	for(i=1;i<=n;++i)
	{
		for(j=1;j<=m;++j)
		{
			sf+=a[i][j];
		//	printf("%d ",a[i][j]);
		}
	 //	printf("\n");
	}
	printf("%ld\n",sf);
	return 0;
}