Find The Shortest Mate

Can you find the shortest mate? The main line has beautiful final position.

1rnr3b/2R5/Q5B1/2p5/1pN5/1k6/3nN1K1/7R w - - 0 1

Comments
No. 1-1
Alena
Alena

1.Ra7 Nxa7
2.Ra1 Bxa1
3.Qa2!+ Kxa2
4.Nc1#

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