Unusual endgame

White to move and win. How should White proceed? No computer analysis please. See if you can figure the solution out on your own.

Hint: This is quite a complicated and lengthy endgame.

B1k5/5P2/3p1rPp/3R4/3p4/6K1/6p1/8 w - - 0 1

Maksimovskikh, 1977