type
    matrice=array[1..100,1..100] of integer;
var i,j,n,m,s,max,aux:integer;
    f,g:text;
    a:matrice;
begin
assign(f,'flip.in');reset(f);
assign(g,'flip.out');rewrite(g);
readln(f,n,m);
s:=0;max:=0;
for i:=1 to n do begin
 for j:=1 to m do
   read(f,a[i,j]);
   readln(f);
end;
for i:=1 to n do begin
  for j:=1 to m do begin
   if a[i,j]>=0 then
    s:=s+a[i,j];
   end;
  end;
max:=s;
for i:=1 to n do begin
  for j:=1 to m do begin
   s:=s+(a[i,j]*-1);
   if max<s then begin
    max:=aux;
    aux:=s;
    s:=max;
    end;
    end;
    end;
  writeln(g,max);
close(f);
close(g);
end.