#include <cstdio>

const int NMax= 17;
int v[NMax][NMax],pm[NMax],smax = -1,n,m;
FILE *in,*out;

void citire () {
	in = fopen ("flip.in", "r");
	out = fopen ("flip.out","w");
	
	fscanf (in,"%d%d", &n,&m);
	
	for (int i=1,j=1;i<=n;fscanf (in,"%d",v+i*NMax +j),i=(j==m)?i+1:i,j=(j==m)?1:j+1);
}

void procesare () {
	
}

void bkt (int *v) {
	if (v == pm + m + 1) {
		procesare();
		return;
	}
	
	*v = 1;
	bkt(v+1);
	*v = -1;
	bkt(v+1);
}

void scriere () {
	fprintf (out,"%d",smax);
	
	fclose(in);
	fclose(out);
}

int main () {
	citire ();
	
	/*for (int i = 1; i <= n; ++i) {
		for (int j = 1; j <= m; ++j) {
			fprintf (out,"%d ", **(v+i*NMax+j));
		}
		fputs("\n",out);
	}*/
	
	bkt (pm + 1);
	
	scriere();
	return 0;
}