program euler;
  const nmax=100000;
      inf=1 shl 30;
  type lista=^celula;
        celula=record
           info:longint;
           pred:lista;
           end;
  var a:array[1..nmax] of lista;
      gr:array[1..nmax] of longint;
      n,m,x,y,i,j:longint;
      r:lista;
      ok:boolean;

  procedure euler(v:longint);
   var w:longint;
      r:lista;
   begin
     while a[v]<>nil do
       begin
         w:=a[v]^.info;
         a[v]:=a[v]^.pred;
         r:=a[w];
         if r^.info=v then a[w]:=a[w]^.pred
           else
            begin
             while r^.pred^.info<>v do r:=r^.pred;
             r^.pred:=r^.pred^.pred;
             end;
         euler(w);
       end;
     write(v,' ');
   end;







  begin
   assign(input,'ciclueuler.in');
   assign(output,'ciclueuler.out');
   reset(input);
   rewrite(output);
   readln(n,m);
   for i:=1 to m do
     begin
      readln(x,y);
      inc(gr[x]);
      inc(gr[y]);
      new(r);
      r^.info:=y;
      r^.pred:=a[x];
      a[x]:=r;
      new(r);
      r^.info:=x;
      r^.pred:=a[y];
      a[y]:=r;
     end;
   ok:=true;
   for i:=1 to n do
     if gr[i] mod 2=1 then ok:=false;
   if  not ok then writeln(-1)
      else euler(1);
   close(output);
  end.