If no candidates has received a majority of votes according to Section 17, first sentence, a second round of voting (final round) shall be held on the fourth Sunday following the first round of voting, confronting the two candidates having received the most valid votes in the first round of voting; if the first round of voting was not held on a Sunday, the second round of voting shall be held on the fifth Sunday following the first round of voting. In case of equal numbers of votes, the federal returning officer shall draw lots to determine the participants in the final round.