<?php

	function fibonacci( $n ) {
    	$V5   = sqrt( 5 );
		$Phi  = ( 1 + $V5 ) / 2;
		$iPhi = -1 / $Phi;
    	return round( ( pow( $Phi, $n ) - pow( $iPhi, $n ) ) / $V5 );
	}
	
	echo fibonacci( 1 ).PHP_EOL;
	echo fibonacci( 5 ).PHP_EOL;
	echo fibonacci( 100 ).PHP_EOL;

?>