#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream f("flip.in");
    ofstream g("flip.out");

    int N,M,i,j,s=0;
    f>>N>>M;
    int a[N][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)
            s=s+a[i][j];
        }
    }
    g<<s;

    return 0;
}