<?php

$input = trim(fgets(STDIN));

for($j =1; $j <=10; $j ++){
    $itemList[$j] = 0;
}

for($i = 1; $i <= $input; $i ++){
    $inputItem = trim(fgets(STDIN));
    $explode = explode(" ", $inputItem);
    foreach($explode as $explodeKey => $explodeValue){
        foreach($itemList as $itemListKey => $itemListValue){
            if($explodeValue == $itemListKey){
                $itemList[$explodeValue] ++;
            }
        }
    }
}

$answerCount = 0;
$answerAmari = 0;

for($p = 1; $p <= 10; $p ++){
    $itemListAnswer = floor($itemList[$p] / 2);
    if($itemList[$p] % 2 !== 0){
       $answerCount += $itemListAnswer;
       $answerAmari += $itemList[$p] - ($itemListAnswer * 2);
    }else if($itemListAnswer >= 1){
       $answerCount += $itemListAnswer;
    }else if($itemListAnswer <= 0){
       $itemListAmariAnswer = floor($itemList[$p] % 2);
       $answerAmari += $itemListAmariAnswer;
    }else{
       $answerAmari += 1;
    }
}

$answerAmari4 = floor($answerAmari / 4);
$answerCount += $answerAmari4;

echo $answerCount."\n";