#include <cstdio>
#include <cmath>
#define FOR(i, a, b)  for (int i = (int)(a); i <= (int)(b); ++ i)
using namespace std;
int a[16][16];
int main()
{
 freopen ("flip.in", "r", stdin);
 freopen ("flip.out", "w", stdout);
 int n, i, j, m, k;
 int sumN , sumpoz;
 scanf ("%d %d", &n, &m);
 FOR (i,1,n)
 FOR (j,1,m) scanf ("%d", &a[i][j]);
  FOR (i,1,n){
     sumpoz = 0 ; sumN = 0 ;
     FOR (j,1,m){
         if (a[i][j]<0)
            sumN+=a[i][j];
         else sumpoz+=a[i][j];}
if (abs(sumN)>sumpoz){
        for (k=1;k<=m;k++) a[i][k]=a[i][k]*-1;

 }
}
int auxi;
FOR (i,1,m){
    sumpoz = 0 , sumN = 0 ;
    auxi = i;
    for (;auxi<=n;auxi++){
            if (a[auxi][i]<0) sumN+=a[auxi][i];
    else sumpoz+=a[auxi][i];}
    if (abs(sumN)>sumpoz){
            for (k=1;k<=n;k++) a[k][i]=a[k][i]*(-1);}
    }
int sum = 0 ;
FOR (i,1,n)
FOR (j,1,m) sum+=a[i][j];
printf ("%d", sum);
}