program flip;
var mat:array[1..50,1..50]of longint;
    m,n,i,j,s1,s2:integer;
    f,g:text;

procedure citire;
begin
readln(f,n,m);
for i:=1 to n do
 for j:=1 to m do read(f,mat[i,j]);
end;

procedure inloc2;
begin
for i:=1 to n do
 begin
 s1:=0;
 s2:=0;
 for j:=1 to m do
  if(mat[i,j]<0)then s1:=s1+mat[i,j]
                else s2:=s2+mat[i,j];
  if s1*(-1)>s2 then for j:=1 to m do mat[i,j]:=mat[i,j]*(-1);
 end;
end;

procedure inloc1;
begin
s1:=0;
s2:=0;
for j:=1 to m do
 begin
  s1:=0;
  s2:=0;
  for i:=1 to n do
  if(mat[i,j]<0)then s1:=s1+mat[i,j]
                else s2:=s2+mat[i,j];
  if s1*(-1)>s2 then for i:=1 to n do mat[i,j]:=mat[i,j]*(-1);
 end;
end;

procedure suma;
var s:longint;
begin
s:=0;
for i:=1 to n do
 for j:=1 to m do s:=s+mat[i,j];
write(g,s);
end;

begin
assign(f,'flip.in');
reset(f);
assign(g,'flip.out');
rewrite(g);
citire;
inloc2;
inloc1;
suma;
close(f);
close(g);
end.