type matrice=array[1..16,1..16] of longint;
     tip=1..16;
var a:matrice;
    n,m,i,j:tip;
    f,g:text;
    s:longint;
    procedure fbi2(var a:matrice;x,y:tip);
     var ok:boolean;
        s:longint;
        k:tip;
    begin
             s:=0;
          for k:=1 to n do
           s:=s+a[k,y];
        if s<0 then
          begin
      for k:=1 to  n do
        a[k,y]:=a[k,y]*(-1);
           end;
     end;
    procedure fbi(var a:matrice;x,y:tip);
    var ok:boolean;
        s:longint;
        k:tip;
    begin
             s:=0;
          for k:=1 to m do
           s:=s+a[x,k];
        if s<0 then
          begin
      for k:=1 to  m do
        a[x,k]:=a[x,k]*(-1);
           end;
     end;
begin

        assign(f,'filip.in');
        reset(f);
        readln(f,n,m);
        for i:=1 to n do
            begin
            for j:=1 to m do
           read(f,a[i,j]);
           readln(f);
             end;
         close(f);
     for i:=1 to n do
          begin
          for j:=1 to m do
      if a[i,j]<0 then fbi(a,i,j);
           end;
          for i:=1 to n do
              begin
              for j:=1 to m do
              if a[i,j]<0 then fbi2(a,i,j);
              end;
           s:=0;
         for i:=1 to n do
             begin
             for j:=1 to m do
             s:=s+a[i,j];
             end;

   assign(g,'filip.out');
   rewrite(g);
        write(g,s);
    close(g);
readln;
end.