www.example.com/a-292-some-text-here  // 292
www.example.com/a-2-asdfss       // 2
www.example.com/a-44-333      // 44
	
string input = "www.example.com/a-292-some-text-here";
Match match = Regex.Match(input, @"d+");
if (match.Success)
{
    int id = int.Parse(match.Value);
    // Use the id...
}
else
{
    // Error!
}