#include <iostream>
#include <fstream>
using namespace std;

int main(){
    ifstream in("flip.in");
    ofstream out("flip.out");
    int c,r,sum=0;
    in >> r >>c;
    int m[r][c];
    for(int i =1; i<=r;i++)
        for(int h=1;h<=c;h++)
            in >> m[i][h];
    for(int i =1; i<=r;i++)
        for(int h=1;h<=c;h++)
            if(m[i][h] >=0)
                sum += m[i][h];
    out << sum;
    return 0;

}