#include<stdio.h>
int a[10][10];
int main()
{int i, j, S=0, n, m, k, l, S1, S2;
FILE *f=fopen ("flip.in","r");
FILE *g=fopen ("flip.out","w");
fscanf (f, "%d %d", &n, &m);
for (i=1;i<=m;i++) for (j=1;j<=n;j++) fscanf (f, "%d", &a[i][j]);
for (i=1;i<=m;i++) {S1=0; S2=0;
		    for (j=1;j<=n;j++) if (a[i][j]>0) S1+=a[i][j];
				       else S2+=a[i][j];
		    if (S1<S2) for (k=1;k<=n;k++) a[i][k]=a[i][k]*(-1);
		    }
for (i=1;i<=m;i++) {S1=S2=0;
                    for (j=1;j<=n;j++) if (a[j][i]>0) S1+=a[j][i];
				      else S2+=a[j][i];
		    if (S1<S2) for (l=1;l<=m;l++) a[j][l]*=(-1);}		        

for (i=1;i<=m;i++) for (j=1;j<=n;j++) S+=a[i][j];
fprintf (g, "%d", S);
fclose(f);
fclose(g);
return 0;
}