How to fix product count switching in js OpenCart category?

Question

JavaScript

Need to switch the number of products in a category when adding to cart. Works only on the first product, further +- does not work.
How can I fix it, I'm not friends with js. Help pliz

Code:

spoiler

<div class="quantity-box quantity_category">
  					<input type="button" id="minus" value="-" class="form-control">         
  					<input type="text" name="quantity" value="1" size="2" id="input-quantity-<?php echo $product['product_id']; ?>"  class="form-control input-quantity">
  					<input type="button" id="plus" value="+" class="form-control">
</div>

<script type="text/javascript"><!--
var minimum = 1;
  $(".input-quantity").change(function(){
    if ($(this).val() < minimum) {
      alert("Minimum Quantity: "+minimum);
      $(".input-quantity").val(minimum);
    }
  });
  // increase number of product
  function minus(minimum){
      var currentval = parseInt($(".input-quantity").val());
      $(".input-quantity").val(currentval-1);
      if($(".input-quantity").val() <= 0 || $(".input-quantity").val() < minimum){
          alert("Minimum Quantity: "+minimum);
          $(".input-quantity").val(minimum);
     }
  };
  // decrease of product
  function plus(){
      var currentval = parseInt($(".input-quantity").val());
     $(".input-quantity").val(currentval+1);
  };
  $('#minus').click(function(){
    minus(minimum);
  });
  $('#plus').click(function(){
    plus();
  });
//--></script>