- fscanf: documentation ( source)
- substr_count: documentation ( source)
- var_dump: documentation ( source)
<?php
fscanf(STDIN, "%d", $n);
$c = 0;
$array = [];
for($i=1;$i<=1000000000;$i++) {
$c += substr_count($i, 1);
$array[$i] = $c;
}
var_dump($array);
echo $c . "\n";