Which year did Denmark, Austria and the UK join the Eurovision Song Contest for the first time?

Explanation

The Eurovision Song Contest was organised for the first time in 1956 in Lugano, Switzerland, mainly as a radio programme, and lasted 1 hour 40 minutes. 7 countries participated in the first contest: The Netherlands, Belgium, Switzerland, Germany, France, Italy and Luxemburg. Denmark, Austria and the UK signed up too late and had to wait until the year after.