#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream fin("flip.in");
    ofstream fout("flip.out");
    int n,m,a[100][100],sp=0,sn=0,i,j;
    fin>>n>>m;
    for(i=0;i<n;i++)
        for(j=0;j<m;j++)
    {
        fin>>a[i][j];
        if(a[i][j]>0)sp+=a[i][j];
        else sn+=a[i][j];
    }
    sn=-sn;
    if(sn>sp)fout<<sn;
    else fout<<sp;
    return 0;
}