Find Sum of Series 1/12+1/22+1/32+1/42+…………

<?php
echo"enter n";
$n=fgets(STDIN);
$sum=0;
for($count=1,$c=12;$count<=$n;$count++)
{
$sum=$sum+(1/$c);
$c=$c+10;

}
echo "Sum of the series=".$sum;

?>