/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
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*******************************************************************************/

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

    return 0;
}