Put your finger on any red card. Move it left or right to the nearest black card. Move it up or down to the nearest red card. Move it diagonally to the nearest black card. Now move it down or to the right to the nearest red card. You’ll always land on the ace of diamonds. (From Harold R. Jacobs, Mathematics: A Human Endeavor, 1970.)

The General Yermolov Cadet School in the southern Russian city of Stavropol is a state-run institution that teaches military and patriotic classes in addition to a normal syllabus. The school allows its pupils to take part in field-training trips, during which they spend a night in a base and undergo physical drills and weapons training. The outings are seen as a treat for students, and those with bad grades are not allowed to go. The school is named after the Russian imperial general Alexei Yermolov and many of its students are from military backgrounds. Photographs by Eduard Korniyenko