I inspected the tires of the bike and found their size: 700 x 40 - 28 x 1 5/8. Which probably means, that the diameter is 28 inches and the tire width is 40 mm (I measured with a ruler).
I found, that people recommend SKS Chromoplastic fenders and they have many sizes: http://www.ebay.com/itm/SKS-Chromoplastic-Road-Racing-Bike-Mudguards-P35-Black-/380993168162?pt=UK_SportGoods_CyclAcces_RL&hash=item58b4f66322
The seller says, that the fender is for 700C (which is probably my size), but the width is not specified. Maybe, 'P35' means 35mm tire?
Should I select the fender exactly for 40mm or buy a little bigger?