ANSWER: RUSSIA

"The Diomede Islands are located in the middle of the Bering Strait between mainland Alaska and Siberia, with the Chukchi Sea to the north and the Bering Sea to the south. 9.3 km (5.8 mi) to the southeast is Fairway Rock, which is generally not considered part of the Diomede Islands. The islands are sometimes called Tomorrow Island (Big Diomede) and Yesterday Isle (Little Diomede) because the time in Big Diomede is 20 hours (approximately a day) ahead of Little Diomede.

The islands are separated by an international border, which is also part of the International Date Line, approximately 2 km (1 mi) from each island, at 168°58'37"W. At the closest distance between Little Diomede and Big Diomede, the two islands are about 3.8 km (2.4 mi) apart. The small habitation on Little Diomede Island is centered on the west side of the island at the village of Diomede.

The Big Diomede Island is considered the easternmost point of Russia."

  - Wikipedia