Explanation: The Russian Orthodox Church used the 'Julian Calendar', which predates the Catholic 'Gregorian Calendar' which corrected the distribution of leap years to fit the solar year more precisely, The Russian Empire, likewise, used the Julian Calendar due to its close association with the Orthodox Church, even after most Catholic and Protestant nations had adopted the more accurate Gregorian Calendar.
... this could lead to some confusion when traveling between countries/cultures, like in 1908, when the Russian Olympics team arrived late and was unable to compete in several of the early events.