In what year did the Central and Eastern European countries first participate in the Eurovision Song Contest?

Explanation

On 1 January 1993, OIRT, the Central and Eastern European version of EBU, merged with the European Broadcasting Union, and the number of potential participating countries thus went up significantly. This has resulted in new qualification rules to keep the number of countries in the final to 25. From 2000 onwards the "Big Four" - the UK, France, Germany and Spain - have been guaranteed a spot in the final, alongside last year's winner.