After Alexander, there were Macedonian kings for 295 years, until the death of queen Cleopatra, who reigned in about the 187th Olympiad [32-29 B.C.].
In her time, Augustus was emperor of the Romans, who was called Sebastos in Greek.
(71) [Cleopatra died] in the 15th year of Augustus' reign.
From then until the 202nd Olympiad [29-32 A.D.], and the 15th year of Tiberius Caesar, there are 52 years.
And from then until the 20th anniversary of Constantinus, there are 300 years.