Hunt for jam announced in Omsk

For which purpose could jam serve? Of course, for eating. Or for something else? The dwellers of the city of Omsk are trying to guess. While the reason of their perplexity is the following.

The question is that one of the city trading houses announced an unusual action in August: every client, who brings a jar of jam to the shop, receives discounts while buying home equipment.

Is now jam in a greater demand than home equipment? It could hardly be so. To be short, the Omsk citizens have not been puzzled by this business mystery, but they bring jam to the shop anyway.