Acting President during temporary absence of President
Section 145 · 1999 Constitution (2004 edition)
What Constitution says
Whenever the President transmits to the President of the Senate and the Speaker of the House of Representatives a written declaration that he is proceeding on vacation or that he is otherwise unable to discharge the functions of his office, until he transmits to them a written declaration to the contrary such functions shall be discharged by the Vice-President as Acting President.
This is the 1999 Constitution as published in 2004. Later amendments aren't included yet, so a section may have changed since.
Original source
Official Gazette · CFRN 1999 official PDF · printed page 73. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections