#include <iostream>
#include <fstream>

using namespace std;

int n, m, a, S = 0;
ifstream in("flip.in");
ofstream out("flip.out");

int main()
{
    in >> n >> m;

    for(int i = 1;i<=n;++i){
        for(int j = 1;j<=m;++j){
            in >> a;
            if(a >= 0){
                S += a;
            }
        }
    }

    out << S << endl;
}