The University of Tokyo was formed in 1877 when the Tokyo Kaisei School and Tokyo Medical School merged to created the faculties of law, science, letters and medicine, which came together with a university preparatory school. Since then the University of Tokyo has merged with a number of schools and institutions to grow into a large research university. It is made up of 10 faculties, 15 graduate schools, 11 affiliated research institutes, 13 university-wide centres, three affiliated libraries and two institutes for advanced study and the University of Tokyo Hospital. The university has just over 450 international exchange agreements with universities from all over the world. The University of Tokyo can count eight Nobel prize winners, 15 Japanese prime ministers and five astronauts among its alumni.