<?php
$num = trim(fgets(STDIN));
$array = array();
for ( $in=0; $in<$num; $in++ ) {
	$array = array_merge($array, explode(" ", trim(fgets(STDIN))));
}

$count = array_count_values($array);
$items = count($array);
$powerup = 0;
foreach ( $count as $index => $value ) {
	if ( $value >= 2 ) {
		$use = floor($value / 2);
		$items -= $use*2;
		$powerup += $use;
	}
}
$powerup += floor($items / 4);

echo $powerup.PHP_EOL;