The army defending Constantinople was relatively small, totaling about 7,000 men, 2,000 of whom were foreigners. At the onset of the siege, probably fewer than 50,000 people were living within the walls, including the refugees from the surrounding area.:32  Turkish commander Dorgano, who was in Constantinople in the pay of the Emperor, was also guarding one of the quarters of the city on the seaward side with the Turks in his pay. These Turks kept loyal to the Emperor and perished in the ensuing battle. The defending army's Genoese corps were well trained and equipped, while the rest of the army consisted of small numbers of well-trained soldiers, armed civilians, sailors and volunteer forces from foreign communities, and finally monks. The garrison used a few small-calibre artillery pieces, which nonetheless proved ineffective. The rest of the city repaired walls, stood guard on observation posts, collected and distributed food provisions, and collected gold and silver objects from churches to melt down into coins to pay the foreign soldiers. The Ottomans had a much larger force. Recent studies and Ottoman archival data state that there were about 50,000-80,000 Ottoman soldiers including between 5,000 and 10,000 Janissaries, *70 cannons:139-140 an elite infantry corps, and thousands of Christian troops, notably 1,500 Serbian cavalry that the Serbian lord Đurađ Branković was forced to supply as part of his obligation to the Ottoman sultan—just a few months before, he had supplied the money for the reconstruction of the walls of Constantinople. Contemporaneous Western witnesses of the siege, who tend to exaggerate the military power of the Sultan, provide disparate and higher numbers ranging from 160,000 to 200,000 and to 300,000.

Answer this question based on the article: How many more is the maximum estimate of the number of Janissaries than Serbian cavalry?
8500