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