According to the speaker, how many singers are there in the band of the Beatles?

The Beatles were a mystical happening that many people still don’t understand. Phenomenologists had a ball in 1964 with Beafiemania, a generally harmless form of madness which came from Britain in 1963. The sole cause of Beatlemania is a quartet of young Englishmen known as the Beatles. In the less than one year that they achieved popularity in England to the time they came to America, the Beatles achieved a popularity and following that is unprecedented in the history of show business in England. They became the first recording artists anywhere in the world to have a record become a million-seller before it was release. They became the target of such adoration by their fans that they had to cancel all one-night bookings because of riots in early 1964. Beatlemania had reached unbelievable proportions in England, it became a form of reverse lend-lease and spread to the United States. Capitol records followed the Beetles’ single record with the release of an album, "Meet the Beetles," in late January of 1964. That event was followed by the Beatles themselves, who arrived in New York February 8, 1964 for three appearances with Ed Sullivan.