First factorial in PHP

gistfile1.txt

<?php 

function FirstFactorial($num) {  

  // code goes here
  //when the value of $num is less than or equal to 1, the function will terminate
  if($num <= 1){
      return 1;
  }
  /* the function will call itself repeatedly, each time multiplying the value
  of $num by its own value -1 until the condition of the 
  previous if statement becomes true */
  else{
       return $num * FirstFactorial($num -1);
       
  }
         
}
   
// keep this function call here  
echo FirstFactorial(fgets(fopen('php://stdin', 'r')));  

?>

Looks good.