program flip;
   var f,g:textfile;
   a:array[1..20,1..20] of integer;
   m,n,i,j:byte;
   s,k,sum:integer;
 begin
 assign(f,'flip.in');reset(f);
 assign(g,'flip.out');rewrite(g);
 read(f,m,n);
 s:=0;k:=0;sum:=0;
 for i:=1 to n do
     for j:=1 to m do read(f,a[i,j]);

  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] else
                                                     if a[i,j]<0 then k:=k+a[i,j];
                      end;
                      if abs(s)<abs(k) then for j:=1 to m do a[i,j]:=-1*a[i,j];
                      s:=0;k:=0;
                   end;
 for j:=1 to m do begin
               for i:=1 to n do
                                begin
                                 if a[i,j]>=0 then s:=s+a[i,j] else
                                                     if a[i,j]<0 then k:=k+a[i,j];
                                 end;
                                 if abs(s)<abs(k) then for i:=1 to n do a[i,j]:=-1*a[i,j];
                                s:=0;k:=0;
                  end;
 for i:=1 to n do
            for j:=1 to m do
                      sum:=sum+a[i,j];
 writeln(g,sum);
 close(f);
 close(g);
 end.