var
  map:array[1..50000,0..1000] of word;
  f:array[1..50000000,1..3] of word;
  i,j,k,n,t,a,b,cl,op:longint;
procedure print;
var
  i,l:integer;
  way:array[1..50000] of word;
begin
  i:=op;
  writeln(f[op,3]);
  l:=0;
  while i<>0 do
    begin
      inc(l);
      way[l]:=f[i,1];
      i:=f[i,2];
    end;
  for i:=l downto 1 do writeln(way[i]);
end;
procedure search;
var
  i:integer;
begin
  for i:=1 to map[f[cl,1],0] do
    begin
      inc(op);
      f[op,1]:=map[f[cl,1],i];
      f[op,2]:=cl;
      f[op,3]:=f[cl,3]+1;
      if map[f[cl,1],i]=k then
        begin
          print;
          halt;
        end;
    end;
end;
begin
  readln(n,k);
  for i:=1 to n do
    begin
      readln(a,b);
      inc(map[a,0]);
      map[a,map[a,0]]:=b;
    end;
  cl:=0;
  op:=1;
  f[1,1]:=1;
  f[1,2]:=0;
  f[1,3]:=1;
  repeat
    inc(cl);
    search;
  until cl>op;
  writeln(-1);
end.