#include <iostream>
#include <fstream>
using namespace std;
ifstream f("flip.in");
ofstream g("flip.out");

int main()
{
    int n,m,a[100][100],s=0,i,j;
    f>>n>>m;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            f>>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];
    g<<s;
    return 0;
}