program flip;
var f,g:text;
    a:array[1..16,1..16]of longint;
    n,m,s,s1,sf:longint;
    i,j:word;
begin
        assign(f,'flip.in');reset(f);
        assign(g,'flip.out');rewrite(g);
        read(f,n,m);
        sf:=0;
        for i:=1 to n do
        begin
                for j:=1 to m do
                        read(f,a[i,j]);
        end;
        for i:=1 to n do
        begin
                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>abs(s1)) then sf:=sf+s
                         else
                                begin
                                        for j:=1 to m do
                                           a[i,j]:=(-1)*a[i,j];
                                           sf:=sf+a[i,j];
                                end;

        end;
        write(g,sf);
        close(f);
        close(g);
end.