#include<fstream>
#include<algorithm>
using namespace std;
ifstream f("flip.in");
ofstream g("flip.out");
int n,m,v[260],i,s,d;
int main()
{
    f>>n>>m;
    d=n*m;
    for(i=1;i<=d;++i)
        f>>v[i];
    i=d;
    sort(v+1,v+d+1);
    while(v[i]>0)
    {
        s=s+v[i];
        i--;
    }
    g<<s<<'\n';
    g.close();
    return 0;
}