Seer's Voidstone

Whenever a player casts a spell, you may pay {1}, if you do, look at the top card of target players library and put a charge counter on
Seer's Voidstone.
{u}{t}, Sacrifice Seer's Voidstone: Look at the top X cards of your library, where X is the number of charge counters on Seer's Voidstone. Put one of those cards into your hand and the rest on the bottom of your library in any order.