type matrice=array [1..1000,0..3] of longint;
type vector=array [1..1000] of longint;
var m,n,i,j,c,k:longint;
    f,g:text;
    a,v:matrice;
    b:vector;
begin
assign(f,'critice.in');
reset(f);
assign(g,'critice.out');
rewrite(g);
read(f,n,m);
for i:=1 to m do
    for j:=1 to 3 do begin
                     read(f,a[i,j]);
                     v[a[i,j],j]:=v[a[i,j],j]+1;
                     end;
k:=0;
for i:=1 to m do begin
                   for j:=1 to m do
                                    if v[i,j]>=2 then  if (a[j,1]=i) or (a[j,2]=i) or (a[j,3]=i) then begin
                                                        k:=k+1;
                                                        b[k]:=j;
                                                        end;
                   end;

writeln(g,k);
for i:=1 to k do writeln(g,b[i]);
close(f);
close(g);
end.