<?php

// You know we are in for a wild ride when we give PHP full system resources!

ini_set('memory_limit', '-1');

$input = array_map('intval', explode(",", file_get_contents($argv[1])));

// I wanted to use zero-based indexing but ran into issues.

// array_merge with a dummy value was way easier

$nums = array_flip(array_merge(['$'], $input));

$turn = $n = null;

$i = count($nums);

$update = function($i) {

// stupid closure visibility

global $nums, $n, $turn;

$n = empty($turn) ? 0 : $i - 1 - $turn;

// I learned about null coalescing when making sure ternaries existed

$turn = $nums[$n] ?? null;

$nums[$n] = $i;

};

while ($i <= 2020) {

$update($i++);

}

echo $n . PHP_EOL;

while ($i <= 30000000) {

$update($i++);

}

echo $n . PHP_EOL;

?>