#include <bits/stdc++.h>
using namespace std;

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

int main()
{
    long long a[20][20], m, n, i, j, s = 0, s1;
    fin >> n >> m;
    for (i = 1; i <= n; i ++)
        for (j = 1; j <= m; j ++)
            fin >> a[i][j];
    for (i = 1; i <= n; i ++)
    {
        s1 = 0;
        for (j = 1; j <= m; j ++)
            if (a[i][j] > 0)
                s1 += a[i][j];
        if (s1 > 0)
            s += s1 ;
        else
            s += - s1;
    }
    fout << s;
    return 0;
}