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



}