program pr2;
  var fi,fo:text;
      a:array[1..16,1..16]of integer;
      m,n,i,j,sum,s,s1: integer;
begin
   assign(fi,'flip.in'); reset(fi);
   assign(fo,'flip.out'); rewrite(fo);
   read(fi,n); read(fi,m);  readln(fi);
   for i:=1 to n do
     for j:=1 to m do
        read(fi,a[i,j]);
   for i:=1 to n do
    s:=0;
    s1:=0;
    for j:=1 to m do
     if a[i,j]<0 then s:=s+a[i,j] else s1:=s1+a[i,j];
     if s<-s1 then for j:=1 to m do a[i,j]:=a[i,j]*-1;
     for j:=1 to m do
    s:=0;
    s1:=0;
    for i:=1 to n do
     if a[i,j]<0 then s:=s+a[i,j] else s1:=s1+a[i,j];
     if s<-s1 then for j:=1 to m do a[i,j]:=a[i,j]*-1;
     for i:=1 to n do
     for j:=1 to m do
     if a[i,j]>0 then sum:=sum+a[i,j];
    write(fo,sum);
   close(fi); close(fo);
end.