Julius Caesar adopted a calendar for his Roman empire in 46 BC. It was used by the Christian Church as they adopted holy days and feasts commemorating Christ's birth, death and resurrection, saints' days, the new year, etc. In 1582 Pope Gregory XIII of the Roman Catholic church adopted a calendar that corrected the lack of a few minutes in each year's time, which over centuries amounted to many days. The Eastern Orthodox churches continued with the earlier Julian Calendar. It wasn't until 1918 that the USSR adopted the Gregorian calendar and by that time the discrepancy between the two calendars was 13 days!

In countries of the USSR where religion was denounced, the New Year celebration became the important holiday. They adapted the decorated evergreen tree, and a red-robed grandfather frost (Ded Moroz) and his helper snow maiden, who bring presents in a 3-horse-drawn sleigh. A festive family dinner is held along with fun and perhaps fireworks. Even children are allowed to stay up until midnight. This is held Jan 1 (or Jan 14 if you use the old calendar).
Those who believe in Christ celebrate Christmas on either Dec 25 or Jan 7 depending on which church they belong to. Most Latter-day Saints celebrate on Dec. 25, but if relatives (like grandparents) are members of the Orthodox church the children may get a small gift at home on one day and at the relatives 13 days later!
St. Nicholas, an orphan whose rich parents died, lived in what was then Greece and is now Turkey, and was known for his generosity, his love for children and for sailors. He became a bishop and was later recognized as a saint. He died on Dec 6, 346 and that day became a feast day in his honor. St Nicholas Day is still celebrated with a small gift for children. In Ukraine that day is now Dec 19.

Thus if you are a child here in Ukraine, you may expect gifts, small or large, from Dec 19 through Jan 14! And as adults you can expect holiday parties and days off work at various intervals during the cold short days of winter! The Kyiv temple will be closed the afternoon of Dec. 24 and all day on Dec. 25, 31 and Jan 1. We will find ways to celebrate here too.