#include<stdio.h>
long a[10000][10000];
int main()
{int n, m, i, j, S=0, S1=0, S2=0, k, l;
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<=m;j++) fscanf (f, "%d", %a[i][j]);
for (i=1;i<=m;i++) {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][j]*=(-1);
		    S1=0;
		    S2=0;
		    }
for (i=1;i<=m;i++) {S1=0;
		    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][i]*=(-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;
}