On 2 October 1187 the Ayyubid sultan Saladin captured Jerusalem and large parts of the Crusader states. In an effort to reclaim the Outremer estates, the Third Crusade was launched by King Philip II of France, King Richard I of England, and Emperor Frederick I of the Holy Roman Empire in 1189. Frederick departed with a huge army, defeated a Seljuk contingent near Philomelion and captured Iconium, but then drowned in the Göksu River near Silifke in Cilicia. Upon his death, Frederick's German crusading host, totaling perhaps 12,000 to 15,000 men, mostly disbanded and a much smaller contingent led by Frederick's son Duke Frederick V of Swabia continued to the Holy Land, where they joined the Siege of Acre. The crusade ended in the 1192 Treaty of Ramla signed by Sultan Saladin and King Richard Coeur de Lion, establishing a three-years armistice and allowing the Muslims to retain control over Jerusalem, while the Crusaders maintained Acre, Jaffa, and other key coastal cities.
Question: How many separate rulers had collaboratively launched the Third Crusade?
Answer: 3