using System.Text;
using System.Text.RegularExpressions;
public static class StringExtensions
{
 public static bool IsAlphanumeric(this string source)
 {
  Regex pattern = new Regex("[^0-9a-zA-Z]");
  return !pattern.IsMatch(source);
 }
}
// EXAMPLE USAGE
class Program
{
 static void Main(string[] args)
 {
  string testString = Console.ReadLine();
  if (testString.IsAlphanumeric())
   Console.WriteLine("Yep!");
  else
   Console.WriteLine("Nope!");
  Console.ReadKey(); // Wait for key before exiting
 }
}