Capablanca defeated by a chess problem

According to a piece of news contained in the Sept. 30th 1954 issue of the italian magazine"Tempo", (what follows is a synopsis) in 1916 Josè Raùl Capablanca  participated in a solving  chess challenge in Philadelphia. The challenge was won by the composer Charles Promislo who solved all 8 problems in 16 minutes. Capalanca was able to solve seven problems in 19 minutes. The attached "White to play and mate in two" problem (by C. F. Kuiper) was the one he could not solve.
Do you want to try and solve it? Of course you cannot use more than 3 or 4 minutes, the same time Capa had at his disposal.....and you cannot use chess engines of course...:-) 
You can find the solution under the diagram.

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Solution

1.Kg5