How many assassination attempts is Fidel Castro said to have survived?

Explanation

Dr Fidel Alejandro Castro Ruz (born 1926) was Cuba's president until 2008. He came to power in the country in 1959 when, as a leader of the July 26 Movement, he ousted the US-backed president Fulgencio Batista and became Prime Minster. On 3 December 1976, he became president of Cuba. Castro paid particular attention to education and healthcare in the country, but also developed his regime in a totalitarian direction, which led e.g. the US to introduce sanctions. Castro is said to have survived 637 assassination attempts.