#include<fstream.h>
int main()
{             
  ifstream f("flip.in");
  ofstream g("flip.out");
  long N,M,i,j,a,s;
  f>>N>>M;
  s=0;
  for(i=1;i<=N;i++)
  for(j=1;j<=M;j++)
  {
    f>>a;
    if(a>=0) s=s+a;
  }
  g<<s;
  return 0;
}