var p,s,i,j,n,m:longint;f,g:text;a:array[1..16,1..16] of longint;ok:boolean;
begin
assign (f,'flip.in');
reset (f);
assign (g,'flip.out');
rewrite (g);
read (f,n,m);
for i:=1 to n do
  for j:=1 to m do
  read (f,a[i,j]);
s:=0;
for i:=1 to n do
  begin
  for j:=1 to m do
  s:=s+a[i,j];
  if s<0 then begin
              a[i,j]:=a[i,j]*(-1);
              a[i,j-1]:=a[i,j-1]*(-1);
              a[i,j-1]:=a[i,j-1]*(-1);
              ok:=false;
              end;
p:=0;
for i:=1 to n do
  for j:=1 to m do
  p:=p+a[i,j];
write (g,p);
close (g);
end.