#include <stdio.h>
#include <iostream.h>
int main (void) {
FILE *fi, *fo;
fi=fopen("flip.in", "rt");
fo=fopen("flip.out", "wt");
long v[100][100], m, n, i, j, k, s;
fscanf(fi, "%ld %ld", &m, &n);
	for (i=0; i<m; i++) {
		for (j=0; j<n; j++) {
		       fscanf(fi,"%ld", &v[i][j]);

}
}
for (j=0; j<n; j++) {
s=0;

for (i=0; i<m; i++) {

s+=v[i][j];

}
if (s<-s) {
for (k=0; k<m; k++) {
v[k][j]*=-1;
}
}
}
for (i=0; i<m; i++) {
s=0;
for (j=0; j<n; j++) {

s+=v[i][j];

}

if (s<-s) {
for (k=0; k<n; k++) {
v[i][k]*=-1;
}
}
}
s=0;
for (i=0; i<m; i++) {
for (j=0; j<n; j++) {
s+=v[i][j];
}
}
fprintf(fo, "%ld", s);
fclose (fi);
fclose(fo);
return 0;
}