London, as one of the world's global cities, exerts strong influence on its arts, commerce, education, entertainment, fashion, finance, health care, media, tourism and communications. Its GDP (€801.66 billion in 2017) makes it the biggest urban economy in Europe and one of the major financial centres in the world. In 2019 it had the second highest number of ultra high-net-worth individuals in Europe after Paris and the second-highest number of billionaires of any city in Europe after Moscow. With Europe's largest concentration of higher education institutions, it includes Imperial College London in natural and applied sciences, the London School of Economics in social sciences, and the comprehensive University College London. The city is home to the most 5-star hotels of any city in the world. In 2012, London became the first city to host three Summer Olympic Games.