diff --git a/src/calculator/index.html b/src/calculator/index.html
index 0f330c2..95860c6 100644
--- a/src/calculator/index.html
+++ b/src/calculator/index.html
@@ -13,6 +13,6 @@
         }
     </style>
 
-    <input type="number" min="0" placeholder="your ASN" oninput="onAsnInput(this)">
+    <input type="text" placeholder="your ASN" oninput="onAsnInput(this)" onkeypress="return event.charCode >= 48 && event.charCode <= 57">
     <p>Port: <span id="result"></span></p>
 </html>
\ No newline at end of file
diff --git a/src/calculator/script.js b/src/calculator/script.js
index 3594755..b31e76c 100644
--- a/src/calculator/script.js
+++ b/src/calculator/script.js
@@ -1,11 +1,7 @@
 function onAsnInput(inputElement) {
+    inputElement.value = inputElement.value.replace(/(?![0-9])./gmi,'');
+
     let portElement = document.getElementById('result');
-
-    if (inputElement.value == '') {
-        portElement.innerText = '';
-        return;
-    }
-
     portElement.innerText = calculate(inputElement.value);
 }