#include <stdio.h>

using namespace std;
#define FOR(i,n) for (i=1;i<=n;i++)
#define FOR2(i,n,j,m) FOR(i,n) FOR (j,m)
int i,j,n,m,a[20][20],s;
int main()
{
    freopen ("flip.in","r",stdin);
    freopen ("flip.out","w",stdout);
    scanf ("%ld%ld",&n,&m);
    FOR2(i,n,j,m)
            scanf ("%ld",&a[i][j]);
    FOR(i,n)
    {
        s=0;
        FOR (j,m)
            s+=a[i][j];
        if (s<0)
            FOR (j,m)
                a[i][j]*=-1;
    }
    FOR(j,m)
    {
        s=0;
        FOR (i,n)
            s+=a[i][j];
        if (s<0)
            FOR (i,n)
                a[i][j]*=-1;
    }
    s=0;
    FOR2(i,n,j,m)
        s+=a[i][j];
    printf ("%ld",s);
    return 0;
}