#include <iostream>
#include <fstream>

using namespace std;

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

    int N,M,a,s=0,i,f;
    in>>N>>M;

    for (f=1; f<=N; f++)
    {
        for (i=1; i<=M; i++)
        {
            in>>a;
            if (a>=0)
            {
                s=s+a;
            }
        }
    }
    out<<s;

    return 0;
}