#include <iostream>
#include <fstream>
using namespace std;
int n,m,a[20][20],i,j,s;
int main()
{
    ifstream f("flip.in");
    ofstream g("flip.out");
    f>>n>>m;
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=m;j++)
        {
            f>>a[i][j];
        }
    }
     for (j=1;j<=m;j++)
    {
        s=s+a[i][j];
    }
    if (s<0) {for (j=1;j<=n;j++) a[i][j]=a[i][j]*(-1);}
    s=0;
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=m;j++)
        {
            s=s+a[i][j];
        }
    }
    g<<s<<"\n";
    return 0;
}