#include <iostream>
#include <fstream>
using namespace std;
ifstream f("flip.in");
ofstream g("flip.out");
int main()
{
    int n,m,i,j,v[100][100],s=0;
    f>>n>>m;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            f>>v[i][j];
            for(i=1;i<=n;i++)
                for(j=1;j<=m;j++)
                    if(v[i][j]>=0)
                    s=s+v[i][j];
                g<<s;
    return 0;
}