program infoflip;
var n :longint;
var m,c,j,s :integer;
var a :array[1..1000000] of integer;
var f,ff :text;
begin
assign(f,'flip.in');
reset(f);
readln(f,n,m);
for c:=1 to n*m do
begin
readln(f,a[c]);
end;
close(f);
s:=0;
for j:=1 to n*m do
begin
if a[j]>=0 then
s:=s+a[j];
end;
assign(ff,'flip.out');
rewrite(ff);
write(ff,s);
close(ff)
end.