As we know our King is blocked on g8. While it's difficult to distract the opponent's Rook, we can force their King to leave the post!1.Re1+Kd6Has an idea to attack the Rook!1...Kf6Allows the White King to go to the f-file. If instead the Black King goes to f6, it will become a shield, preventing any checks.2.Kf8Ra23.g8=QRa8+4.Re8And White wins.1...Kd8Is the same as 1...Kd71...Kd7Leads to the previous position.2.Re4...2.Kf7 again gets under lot of checks.2....Kd53.Rg4...The Black King is too far and the attacking King gets out either way. On top of that, White's Rook covers the g-file, so the pawn can't be attacked.3.Re7Also wins! But the main line is easier to remember.Kd64.Kf8Ra25.g8=QRa8+6.Re83....Ke63...Rf24.Kh7Rh2+5.Kg6And promotion is unstoppable.4.Kf8Rf2+5.Ke8White promotes and wins!