Austria-Hungary precipitated the Bosnian crisis of 1908-1909 by officially annexing the former Ottoman territory of Bosnia and Herzegovina, which it had occupied since 1878. This angered the Kingdom of Serbia and its patron, the Pan-Slavic and Orthodox Russian Empire. Russian political manoeuvring in the region destabilised peace accords that were already fracturing in the Balkans, which came to be known as the "powder keg of Europe." In 1912 and 1913, the First Balkan War was fought between the Balkan League and the fracturing Ottoman Empire. The resulting Treaty of London further shrank the Ottoman Empire, creating an independent Albanian state while enlarging the territorial holdings of Bulgaria, Serbia, Montenegro, and Greece. When Bulgaria attacked Serbia and Greece on 16 June 1913, it lost most of Macedonia to Serbia and Greece, and Southern Dobruja to Romania in the 33-day Second Balkan War, further destabilising the region. The Great Powers were able to keep these Balkan conflicts contained, but the next one would spread throughout Europe and beyond.
Question: How many countries did Bulgaria attack on June 16, 1913?
Answer: 2