PHP while loop is not working

<?php
$dbc=mysqli_connect('localhost','root','','sam_telephone');


$query="SELECT * FROM master_name";
$result=  mysqli_query($dbc,$query);

$display=mysqli_fetch_array($result);

echo $display['f_name']; /// its show me the result  which is fine 

// but when i apply while loop it does not show any thing.

while($y = mysqli_fetch_array($result)){
    echo $y['f_name'];
}
// $y['f_name'] should give me a result becuase it showing me the result on line
10 why its not working on this line i dont know 



?>