<?php

// opti
$count = 0;
function return_calls(){
    global $count;
    $count++;
    return ($count  % 3 == 0)? $count : null;
}


// opti
function return_calls(){
    static $count = 0;
    $count++;
    return ($count  % 3 == 0)? $count : null;
}

function return_calls(){
    static $count = 0;
    $count++;
    if($count  % 3 == 0){
        return $count;
    }
    else{
        return null;
    }
}
?>