#include <iostream>
#include <fstream>

using namespace std;

ifstream in("flip.in");
ofstream out("flip.out");

int n,m,i,j,s,a[17][17];

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

    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            in>>a[i][j];

    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            if(a[i][j]>=0)
                s=s+a[i][j];

    out<<s;

    return 0;
}