Base64 Decode : MTYwMjM

Input : 
MTYwMjM

Output: 
16023

Example code :

Code PHP - base64_decode():
<?php
  $str = 'MTYwMjM';
  echo base64_decode($str);
?>

Code Python - base64.b64decode() :
<<< import base64
<<< encoded = 'MTYwMjM'
<<< data = base64.b64decode(encoded)
<<< data

Code JavaScript - atob() :
atob('MTYwMjM');

Code C# - System.Convert.FromBase64String() : 
string base64Encoded = "MTYwMjM";
byte[] data = System.Convert.FromBase64String(base64Encoded);
string base64Decoded = System.Text.ASCIIEncoding.ASCII.GetString(data);