#include <iostream>
#include <fstream>

using namespace std;

ifstream fin ("flip.in");
ofstream fout ("flip.out");

int main()
{
    int m, n, a[100][100], s1 = 0, s2 = 0;
    fin >> n >> m;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            fin >> a[i][j];

    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            if (a[i][j] > 0) s1 = s1 + a[i][j];

    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            if (a[i][j] < 0) s2 = s2 + a[i][j] * (-1);

    if (s1 > s2) fout << s1;
    else fout << s2;
}