In case the President wishes to resign, to whom he is to address his resignation letter?

Article 56 of the Indian Constitution states that (1) the President shall hold office for a term of five years from the date on which he enters upon his office: provided that-the President may, by writing under his hand addressed to the Vice-President, resign his office; the President may, for violation of the Constitution, be removed from office by impeachment in the manner provided in article 61; and the President shall, notwithstanding the expiration of his term, continue to hold office until his successor enters upon his office; (2) any resignation addressed to the Vice-President under clause (1) of the proviso to clause (1) shall forthwith be communicated by him to the Speaker of the House of the People.