php html post

if I have the following html in which there is a series of submit buttons and a corresponding text field, which differ only in their names via a counter...

<form name="form_test" method="post" action="PHP_TEST.php">
<input type="text" name="input_1"></input>
<input type="submit" name="submit_1"></input>
<br>
<input type="text" name="input_2"></input>
<input type="submit" name="submit_2"></input>
<br>
<input type="text" name="input_3"></input>
<input type="submit" name="submit_3"></input>
...

I want a php file to be called whenever a sumbit is pressed. My question is how in PHP can I get the value of the corresponding text input whenever its submit button is pressed.

PHP Code:

---

if($_POST['submit_1']){
 // $_POST['input_1']
}elseif($_POST['submit_2']){
 // $_POST['input_2']
}elseif($_POST['submit_3']){
 // $_POST['input_3']
} 


---

Yeah i considered that, but there may be a LOT of these if statements that way. Is there any more simple/elegant way of doing this?