#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("flip.in");
ofstream fout("flip.out");
int main()
{
    int n,m,sp,sn,s=0;
    fin>>n>>m;
    int x[n+1][m+1];

    for(int i=1;i<=n;i++)
    {
        sp=0,sn=0;
        for(int j=1;j<=m;j++)
        {
            fin>>x[i][j];
            if(x[i][j]>=0)sp+=x[i][j];
            else sn+=x[i][j];
        }
        if(-sn>sp)for(int k=1;k<=m;k++)x[i][k]*=-1;
    }

    for(int j=1;j<=m;j++)
    {
        sp=0,sn=0;
        for(int i=1;i<=n;i++)
        {
           if(x[i][j]>=0)sp+=x[i][j];
           else sn+=x[i][j];
        }
        if(-sn>sp)for(int k=1;k<=n;k++)x[k][j]*=-1;
    }

    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
        s+=x[i][j];

    fout<<s;
    return 0;
}