You are seeing a 21-year-old male patient who has presented to you in primary care with a rash, which came on 2 days ago. On examination you note the presence of multiple, discrete, salmon coloured lesions that are slightly raised, circular and slightly scaly. The lesions are not vesicular and are not present on the palms or soles of the feet. Upon further questioning the patient informs you that the rash started with a larger, slightly raised lesion on the trunk. You suspect he is trying to describe a herald patch. What is the most likely diagnosis?