Taken from the official Hellenic Parliament website:
The President of the Republic regulates the functions of the institutions of the Republic (article 30 par. 1).
The President is elected by Parliament and has the right to re-election only once.
The elected President, before assuming his duties, takes, before Parliament, an oath, the form of which is laid down in the Constitution.
The first stage includes three separate ballots:
FIRST BALLOT – 200 VOTES
in the first ballot the votes of a two-thirds majority of the total number of Members of Parliament shall be required
SECOND BALLOT – 200 VOTES
if the said majority is not attained, the ballot shall be repeated after five days, the same majority being required
THIRD BALLOT – 180 VOTES
if once again the required majority is not attained, voting shall be repeated after five days, the person receiving the votes of a three-fifths majority of the total number of Members of Parliament shall be elected President of the Republic.
If the third ballot also fails to produce the required majority, Parliament shall be dissolved within ten days of the vote and elections for a new Parliament shall be called.
The second stage of the procedure shall be conducted by the new Parliament as soon as it has constituted itself as a body and shall include another three successive ballots:
FIRST BALLOT – 180 VOTES
in the first ballot the votes of a three-fifths majority of the total number of Members
of Parliament shall be required
SECOND BALLOT – 151 VOTES
should this majority not be attained, voting shall be repeated within five days and the person receiving an absolute majority of the votes of the total number of Members of Parliament shall be elected President of the Republic
THIRD BALLOT
if the second ballot fails to produce the required majority, then within five days the third and final vote shall take place between the two candidates receiving the highest number of votes. The person who receives a relative majority shall be elected President of the Republic.