Giant panda Ding Ding is seen at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Evgeny Sinitsyn)

Visitors watch Giant panda Ding Ding at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Evgeny Sinitsyn)

Giant panda Ding Ding tastes its birthday cake at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Evgeny Sinitsyn)

Giant panda Ding Ding is seen at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Evgeny Sinitsyn)

Giant panda Ding Ding is seen at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Evgeny Sinitsyn)

Giant panda Ding Ding is seen at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Evgeny Sinitsyn)

Giant panda Ru Yi tries to open its gift box at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Bai Xueqi)

Giant panda Ru Yi tastes its birthday cake at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Bai Xueqi)

Giant panda Ru Yi tastes its birthday cake at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Bai Xueqi)

Children pose for photos with performers during birthday celebrations for two giant pandas at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Bai Xueqi)

Giant panda Ru Yi prepares to taste its birthday cake at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Bai Xueqi)

Giant panda Ding Ding sits beside its birthday cake and gifts at the Moscow Zoo in Moscow, capital of Russia, July 31, 2019. The Moscow Zoo celebrated birthday for two giant pandas Ding Ding and Ru Yi that arrived from China in late April for a 15-year scientific program. (Xinhua/Evgeny Sinitsyn)