#include <iostream>
#include <fstream>
#include <sstream>
using namespace std;
int main()
{
    ifstream in("flip.in");
    ofstream out("flip.out");

    int N,M;
    in >> N >> M;
    long int v[N][M];
    long long int suma = 0;
    long int maxim;
    for(int i =1; i<=N; i++)
        for(int j=1; j<=M; j++)
        {
            in >> v[i][j];
            if(i == 1 && j == 1)
                maxim = v[i][j];
            if(v[i][j] > 0)
                suma += v[i][j];
            if(v[i][j] > maxim)
                maxim = v[i][j];
        }
    if(suma == 0 && maxim <= 0)
        suma = maxim;
    //cout << maxim << endl;
    out << suma;
    return 0;
}