Instructions: Generate a correct and concise answer for the question based on the words in the context.
Input: Context : The Salonika Agreement (also called the Thessaloniki Accord) was a treaty signed on 31 July 1938 between Bulgaria on the one hand and the Balkan Entente--the states of Greece, Romania, Turkey and Yugoslavia--on the other.
Question : What is the date when Salonika Agreement happened?
Output:
31 July 1938